diff --git a/doc/docs.md b/doc/docs.md
index ff23859ff7..3b9d4b8d8f 100644
--- a/doc/docs.md
+++ b/doc/docs.md
@@ -3283,13 +3283,13 @@ fn C.sqlite3_close(&C.sqlite3) int
 fn C.sqlite3_column_int(stmt &C.sqlite3_stmt, n int) int
 
 // ... you can also just define the type of parameter and leave out the C. prefix
-fn C.sqlite3_prepare_v2(&sqlite3, charptr, int, &&sqlite3_stmt, &charptr) int
+fn C.sqlite3_prepare_v2(&C.sqlite3, charptr, int, &&C.sqlite3_stmt, &charptr) int
 
-fn C.sqlite3_step(&sqlite3_stmt)
+fn C.sqlite3_step(&C.sqlite3_stmt)
 
-fn C.sqlite3_finalize(&sqlite3_stmt)
+fn C.sqlite3_finalize(&C.sqlite3_stmt)
 
-fn C.sqlite3_exec(db &sqlite3, sql charptr, cb FnSqlite3Callback, cb_arg voidptr, emsg &charptr) int
+fn C.sqlite3_exec(db &C.sqlite3, sql charptr, cb FnSqlite3Callback, cb_arg voidptr, emsg &charptr) int
 
 fn C.sqlite3_free(voidptr)
 
diff --git a/examples/wkhtmltopdf.v b/examples/wkhtmltopdf.v
index c519ed5211..a5b6b944df 100644
--- a/examples/wkhtmltopdf.v
+++ b/examples/wkhtmltopdf.v
@@ -72,7 +72,7 @@ fn main() {
 	println('wkhtmltopdf_http_error_code: $error_code')
 	if result {
 		data := &charptr(0)
-		size := C.wkhtmltopdf_get_output(converter, &data)
+		size := C.wkhtmltopdf_get_output(converter, data)
 		println('wkhtmltopdf_get_output: $size bytes')
 		mut file := os.open_file('./google.pdf', 'w+', 0o666) or {
 			println('ERR: $err')
diff --git a/vlib/builtin/cfns.c.v b/vlib/builtin/cfns.c.v
index 5cb47e6e39..02e3380e5a 100644
--- a/vlib/builtin/cfns.c.v
+++ b/vlib/builtin/cfns.c.v
@@ -45,9 +45,10 @@ pub fn proc_pidpath(int, voidptr, int) int
 
 fn C.realpath(charptr, charptr) &char
 
-fn C.chmod(byteptr, int) int
+// fn C.chmod(byteptr, mode_t) int
+fn C.chmod(byteptr, u32) int
 
-fn C.printf(byteptr, ...byteptr) int
+fn C.printf(byteptr, ...voidptr) int
 
 fn C.puts(byteptr) int
 
@@ -56,7 +57,7 @@ fn C.fputs(str byteptr, stream &C.FILE) int
 fn C.fflush(&C.FILE) int
 
 // TODO define args in these functions
-fn C.fseek() int
+fn C.fseek(stream &C.FILE, offset int, whence int) int
 
 fn C.fopen(filename charptr, mode charptr) &C.FILE
 
@@ -66,9 +67,9 @@ fn C.fread(ptr voidptr, item_size size_t, items size_t, stream &C.FILE) size_t
 
 fn C.fwrite(ptr voidptr, item_size size_t, items size_t, stream &C.FILE) size_t
 
-fn C.fclose() int
+fn C.fclose(stream &C.FILE) int
 
-fn C.pclose() int
+fn C.pclose(stream &C.FILE) int
 
 // process execution, os.process:
 fn C.getpid() int
@@ -94,25 +95,25 @@ fn C.setenv(charptr, charptr, int) int
 
 fn C.unsetenv(charptr) int
 
-fn C.access() int
+fn C.access(path charptr, amode int) int
 
-fn C.remove() int
+fn C.remove(filename charptr) int
 
-fn C.rmdir() int
+fn C.rmdir(path charptr) int
 
-fn C.chdir() int
+fn C.chdir(path charptr) int
 
-fn C.rewind() int
+fn C.rewind(stream &C.FILE) int
 
 fn C.stat(charptr, voidptr) int
 
-fn C.lstat() int
+fn C.lstat(path charptr, buf &C.stat) int
 
-fn C.rename() int
+fn C.rename(old_filename charptr, new_filename charptr) int
 
-fn C.fgets() int
+fn C.fgets(str charptr, n int, stream &C.FILE) int
 
-fn C.memset() int
+fn C.memset(str voidptr, c int, n size_t) int
 
 fn C.sigemptyset() int
 
@@ -122,18 +123,20 @@ fn C.signal(signal int, handlercb voidptr) voidptr
 
 fn C.mktime() int
 
-fn C.gettimeofday() int
+fn C.gettimeofday(tv &C.timeval, tz &C.timezone) int
 
 [trusted]
-fn C.sleep(int) int
+fn C.sleep(seconds u32) u32
 
-fn C.usleep() int
+// fn C.usleep(usec useconds_t) int
+fn C.usleep(usec u32) int
 
 fn C.opendir(charptr) voidptr
 
-fn C.closedir() int
+fn C.closedir(dirp &C.DIR) int
 
-fn C.mkdir() int
+// fn C.mkdir(path charptr, mode mode_t) int
+fn C.mkdir(path charptr, mode u32) int
 
 // C.rand returns a pseudorandom integer from 0 (inclusive) to C.RAND_MAX (exclusive)
 [trusted]
@@ -141,13 +144,13 @@ fn C.rand() int
 
 // C.srand seeds the internal PRNG with the given value.
 [trusted]
-fn C.srand(seed uint)
+fn C.srand(seed u32)
 
-fn C.atof() int
+fn C.atof(str charptr) f64
 
-fn C.tolower() int
+fn C.tolower(c int) int
 
-fn C.toupper() int
+fn C.toupper(c int) int
 
 [trusted]
 fn C.getchar() int
@@ -155,33 +158,33 @@ fn C.getchar() int
 [trusted]
 fn C.strerror(int) charptr
 
-fn C.snprintf() int
+fn C.snprintf(str charptr, size size_t, format charptr, opt ...voidptr) int
 
 fn C.fprintf(byteptr, ...byteptr)
 
-fn C.WIFEXITED() bool
+fn C.WIFEXITED(status int) bool
 
-fn C.WEXITSTATUS() int
+fn C.WEXITSTATUS(status int) int
 
-fn C.WIFSIGNALED() bool
+fn C.WIFSIGNALED(status int) bool
 
-fn C.WTERMSIG() int
+fn C.WTERMSIG(status int) int
 
-fn C.isatty() int
+fn C.isatty(fd int) int
 
-fn C.syscall() int
+fn C.syscall(number int, va ...voidptr) int
 
-fn C.sysctl() int
+fn C.sysctl(name &int, namelen u32, oldp voidptr, oldlenp voidptr, newp voidptr, newlen size_t) int
 
 fn C._fileno(int) int
 
 fn C._get_osfhandle(fd int) C.intptr_t
 
-fn C.GetModuleFileName() int
+fn C.GetModuleFileName(hModule voidptr, lpFilename &u16, nSize u32) int
 
 fn C.GetModuleFileNameW(hModule voidptr, lpFilename &u16, nSize u32) u32
 
-fn C.CreateFile() voidptr
+fn C.CreateFile(lpFilename &u16, dwDesiredAccess u32, dwShareMode u32, lpSecurityAttributes &u16, dwCreationDisposition u32, dwFlagsAndAttributes u32, hTemplateFile voidptr) voidptr
 
 fn C.CreateFileW(lpFilename &u16, dwDesiredAccess u32, dwShareMode u32, lpSecurityAttributes &u16, dwCreationDisposition u32, dwFlagsAndAttributes u32, hTemplateFile voidptr) u32
 
@@ -203,11 +206,11 @@ fn C.ReadFile(hFile voidptr, lpBuffer voidptr, nNumberOfBytesToRead u32, lpNumbe
 
 fn C.GetFileAttributesW(lpFileName byteptr) u32
 
-fn C.RegQueryValueEx() voidptr
+fn C.RegQueryValueEx(hKey voidptr, lpValueName &u16, lp_reserved &u32, lpType &u32, lpData byteptr, lpcbData &u32) voidptr
 
 fn C.RegQueryValueExW(hKey voidptr, lpValueName &u16, lp_reserved &u32, lpType &u32, lpData byteptr, lpcbData &u32) int
 
-fn C.RegOpenKeyEx() voidptr
+fn C.RegOpenKeyEx(hKey voidptr, lpSubKey &u16, ulOptions u32, samDesired u32, phkResult voidptr) voidptr
 
 fn C.RegOpenKeyExW(hKey voidptr, lpSubKey &u16, ulOptions u32, samDesired u32, phkResult voidptr) int
 
@@ -215,9 +218,9 @@ fn C.RegSetValueEx() voidptr
 
 fn C.RegSetValueExW(hKey voidptr, lpValueName &u16, Reserved u32, dwType u32, lpData byteptr, lpcbData u32) int
 
-fn C.RegCloseKey()
+fn C.RegCloseKey(hKey voidptr)
 
-fn C.RemoveDirectory() int
+fn C.RemoveDirectory(lpPathName charptr) int
 
 // fn C.GetStdHandle() voidptr
 fn C.GetStdHandle(u32) voidptr
@@ -235,33 +238,33 @@ fn C.wprintf()
 // fn C.setbuf()
 fn C.setbuf(voidptr, charptr)
 
-fn C.SymCleanup()
+fn C.SymCleanup(hProcess voidptr)
 
-fn C.MultiByteToWideChar() int
+fn C.MultiByteToWideChar(codePage u32, dwFlags u32, lpMultiMyteStr charptr, cbMultiByte int, lpWideCharStr &u16, cchWideChar int) int
 
-fn C.wcslen() int
+fn C.wcslen(str &u16) int
 
-fn C.WideCharToMultiByte() int
+fn C.WideCharToMultiByte(codePage u32, dwFlags u32, lpWideCharStr &u16, cchWideChar int, lpMultiByteStr charptr, cbMultiByte int, lpDefaultChar charptr, lpUsedDefaultChar &int) int
 
-fn C._wstat()
+fn C._wstat(path &u16, buffer &C._stat)
 
-fn C._wrename() int
+fn C._wrename(oldname &u16, newname &u16) int
 
-fn C._wfopen() voidptr
+fn C._wfopen(filename &u16, mode &u16) voidptr
 
-fn C._wpopen() voidptr
+fn C._wpopen(command &u16, mode &u16) voidptr
 
-fn C._pclose() int
+fn C._pclose(stream &C.FILE) int
 
-fn C._wsystem() int
+fn C._wsystem(command &u16) int
 
-fn C._wgetenv() voidptr
+fn C._wgetenv(varname &u16) voidptr
 
-fn C._putenv() int
+fn C._putenv(envstring charptr) int
 
-fn C._waccess() int
+fn C._waccess(path &u16, mode int) int
 
-fn C._wremove() int
+fn C._wremove(path &u16) int
 
 fn C.ReadConsole(in_input_handle voidptr, out_buffer voidptr, in_chars_to_read u32, out_read_chars &u32, in_input_control voidptr) bool
 
@@ -269,9 +272,9 @@ fn C.WriteConsole() voidptr
 
 fn C.WriteFile() voidptr
 
-fn C._wchdir()
+fn C._wchdir(dirname &u16)
 
-fn C._wgetcwd() int
+fn C._wgetcwd(buffer &u16, maxlen int) int
 
 fn C._fullpath() int
 
@@ -281,25 +284,26 @@ fn C.GetCommandLine() voidptr
 
 fn C.LocalFree()
 
-fn C.FindFirstFileW() voidptr
+fn C.FindFirstFileW(lpFileName &u16, lpFindFileData voidptr) voidptr
 
-fn C.FindFirstFile() voidptr
+fn C.FindFirstFile(lpFileName byteptr, lpFindFileData voidptr) voidptr
 
-fn C.FindNextFile() int
+fn C.FindNextFile(hFindFile voidptr, lpFindFileData voidptr) int
 
-fn C.FindClose()
+fn C.FindClose(hFindFile voidptr)
 
-fn C.MAKELANGID() int
+// macro
+fn C.MAKELANGID(lgid voidptr, srtid voidptr) int
 
-fn C.FormatMessage() voidptr
+fn C.FormatMessage(dwFlags u32, lpSource voidptr, dwMessageId u32, dwLanguageId u32, lpBuffer voidptr, nSize int, Arguments ...voidptr) voidptr
 
 fn C.CloseHandle(voidptr) int
 
-fn C.GetExitCodeProcess()
+fn C.GetExitCodeProcess(hProcess voidptr, lpExitCode &u32)
 
 fn C.GetTickCount() i64
 
-fn C.Sleep()
+fn C.Sleep(dwMilliseconds u32)
 
 fn C.WSAStartup(u16, &voidptr) int
 
diff --git a/vlib/clipboard/clipboard_windows.c.v b/vlib/clipboard/clipboard_windows.c.v
index b1f696d7bd..f78566e0ca 100644
--- a/vlib/clipboard/clipboard_windows.c.v
+++ b/vlib/clipboard/clipboard_windows.c.v
@@ -20,7 +20,7 @@ struct WndClassEx {
 	h_icon_sm       &u16
 }
 
-fn C.RegisterClassEx(class WndClassEx) int
+fn C.RegisterClassEx(class &WndClassEx) int
 
 fn C.GetClipboardOwner() &C.HWND
 
@@ -35,9 +35,9 @@ fn C.GlobalAlloc(uFlag u32, size i64) C.HGLOBAL
 
 fn C.GlobalFree(buf C.HGLOBAL)
 
-fn C.GlobalLock(buf C.HGLOBAL)
+fn C.GlobalLock(buf C.HGLOBAL) voidptr
 
-fn C.GlobalUnlock(buf C.HGLOBAL)
+fn C.GlobalUnlock(buf C.HGLOBAL) bool
 
 fn C.SetClipboardData(uFormat u32, data voidptr) C.HANDLE
 
@@ -174,8 +174,8 @@ pub fn (mut cb Clipboard) get_text() string {
 		C.CloseClipboard()
 		return ''
 	}
-	str := unsafe { string_from_wide(&u16(C.GlobalLock(h_data))) }
-	C.GlobalUnlock(h_data)
+	str := unsafe { string_from_wide(&u16(C.GlobalLock(C.HGLOBAL(h_data)))) }
+	C.GlobalUnlock(C.HGLOBAL(h_data))
 	return str
 }
 
diff --git a/vlib/clipboard/x11/clipboard.c.v b/vlib/clipboard/x11/clipboard.c.v
index bd00fbef26..ac632d7f7d 100644
--- a/vlib/clipboard/x11/clipboard.c.v
+++ b/vlib/clipboard/x11/clipboard.c.v
@@ -25,45 +25,45 @@ struct C.Window {
 
 fn C.XInitThreads() int
 
-fn C.XCloseDisplay(d &Display)
+fn C.XCloseDisplay(d &C.Display)
 
-fn C.XFlush(d &Display)
+fn C.XFlush(d &C.Display)
 
-fn C.XDestroyWindow(d &Display, w C.Window)
+fn C.XDestroyWindow(d &C.Display, w C.Window)
 
-fn C.XNextEvent(d C.Display, e &XEvent)
+fn C.XNextEvent(d &C.Display, e &C.XEvent)
 
-fn C.XSetSelectionOwner(d &Display, a C.Atom, w C.Window, time int)
+fn C.XSetSelectionOwner(d &C.Display, a C.Atom, w C.Window, time int)
 
-fn C.XGetSelectionOwner(d &Display, a C.Atom) C.Window
+fn C.XGetSelectionOwner(d &C.Display, a C.Atom) C.Window
 
-fn C.XChangeProperty(d &Display, requestor C.Window, property C.Atom, typ C.Atom, format int, mode int, data voidptr, nelements int) int
+fn C.XChangeProperty(d &C.Display, requestor C.Window, property C.Atom, typ C.Atom, format int, mode int, data voidptr, nelements int) int
 
-fn C.XSendEvent(d &Display, requestor C.Window, propogate int, mask i64, event &XEvent)
+fn C.XSendEvent(d &C.Display, requestor C.Window, propogate int, mask i64, event &C.XEvent)
 
-fn C.XInternAtom(d &Display, typ byteptr, only_if_exists int) C.Atom
+fn C.XInternAtom(d &C.Display, typ byteptr, only_if_exists int) C.Atom
 
-fn C.XCreateSimpleWindow(d &Display, root C.Window, x int, y int, width u32, height u32, border_width u32, border u64, background u64) C.Window
+fn C.XCreateSimpleWindow(d &C.Display, root C.Window, x int, y int, width u32, height u32, border_width u32, border u64, background u64) C.Window
 
 fn C.XOpenDisplay(name byteptr) &C.Display
 
-fn C.XConvertSelection(d &Display, selection C.Atom, target C.Atom, property C.Atom, requestor Window, time int) int
+fn C.XConvertSelection(d &C.Display, selection C.Atom, target C.Atom, property C.Atom, requestor C.Window, time int) int
 
-fn C.XSync(d &Display, discard int) int
+fn C.XSync(d &C.Display, discard int) int
 
-fn C.XGetWindowProperty(d &Display, w Window, property C.Atom, offset i64, length i64, delete int, req_type C.Atom, actual_type_return &C.Atom, actual_format_return &int, nitems &u64, bytes_after_return &u64, prop_return &byteptr) int
+fn C.XGetWindowProperty(d &C.Display, w C.Window, property C.Atom, offset i64, length i64, delete int, req_type C.Atom, actual_type_return &C.Atom, actual_format_return &int, nitems &u64, bytes_after_return &u64, prop_return &byteptr) int
 
-fn C.XDeleteProperty(d &Display, w Window, property C.Atom) int
+fn C.XDeleteProperty(d &C.Display, w C.Window, property C.Atom) int
 
-fn C.DefaultScreen() int
+fn C.DefaultScreen(display &C.Display) int
 
-fn C.RootWindow() voidptr
+fn C.RootWindow(display &C.Display, screen_number int) C.Window
 
-fn C.BlackPixel() voidptr
+fn C.BlackPixel(display &C.Display, screen_number int) u32
 
-fn C.WhitePixel() voidptr
+fn C.WhitePixel(display &C.Display, screen_number int) u32
 
-fn C.XFree()
+fn C.XFree(data voidptr)
 
 fn todo_del() {}
 
@@ -404,7 +404,7 @@ fn read_property(d &C.Display, w C.Window, p C.Atom) Property {
 		if ret != 0 {
 			C.XFree(ret)
 		}
-		C.XGetWindowProperty(d, w, p, 0, read_bytes, 0, C.AnyPropertyType, &actual_type,
+		C.XGetWindowProperty(d, w, p, 0, read_bytes, 0, C.Atom(C.AnyPropertyType), &actual_type,
 			&actual_format, &nitems, &bytes_after, &ret)
 		read_bytes *= 2
 		if bytes_after == 0 {
diff --git a/vlib/crypto/rand/rand_darwin.c.v b/vlib/crypto/rand/rand_darwin.c.v
index e42e762869..c642ee4b28 100644
--- a/vlib/crypto/rand/rand_darwin.c.v
+++ b/vlib/crypto/rand/rand_darwin.c.v
@@ -8,12 +8,12 @@ module rand
 
 #flag darwin -framework Security
 
-fn C.SecRandomCopyBytes() int
+fn C.SecRandomCopyBytes(rnd C.SecRandomRef, count size_t, bytes voidptr) int
 
 // read returns an array of `bytes_needed` random bytes read from the OS.
 pub fn read(bytes_needed int) ?[]byte {
 	mut buffer := []byte{ len: bytes_needed }
-	status := C.SecRandomCopyBytes(0, bytes_needed, buffer.data)
+	status := C.SecRandomCopyBytes(C.SecRandomRef(0), bytes_needed, buffer.data)
 	if status != 0 {
 		return read_error
 	}
diff --git a/vlib/dl/dl_windows.c.v b/vlib/dl/dl_windows.c.v
index 631ece2b4a..e057f186ae 100644
--- a/vlib/dl/dl_windows.c.v
+++ b/vlib/dl/dl_windows.c.v
@@ -5,9 +5,9 @@ pub const (
 	rtld_lazy = 0
 )
 
-fn C.LoadLibrary(libfilename C.LPCWSTR) voidptr
+fn C.LoadLibrary(libfilename &u16) voidptr
 
-fn C.GetProcAddress(handle voidptr, procname C.LPCSTR) voidptr
+fn C.GetProcAddress(handle voidptr, procname byteptr) voidptr
 
 fn C.FreeLibrary(handle voidptr) bool
 
diff --git a/vlib/mysql/_cdefs.c.v b/vlib/mysql/_cdefs.c.v
index c3baa13458..5fe43733d3 100644
--- a/vlib/mysql/_cdefs.c.v
+++ b/vlib/mysql/_cdefs.c.v
@@ -34,7 +34,7 @@ struct C.MYSQL_FIELD {
 
 fn C.mysql_init(mysql &C.MYSQL) &C.MYSQL
 
-fn C.mysql_real_connect(mysql &C.MYSQL, host byteptr, user byteptr, passwd byteptr, db byteptr, port u32, unix_socket byteptr, clientflag u64) &C.MYSQL
+fn C.mysql_real_connect(mysql &C.MYSQL, host charptr, user charptr, passwd charptr, db charptr, port u32, unix_socket charptr, client_flag ConnectionFlag) &C.MYSQL
 
 fn C.mysql_query(mysql &C.MYSQL, q byteptr) int
 
@@ -56,13 +56,13 @@ fn C.mysql_num_fields(res &C.MYSQL_RES) int
 
 fn C.mysql_num_rows(res &C.MYSQL_RES) u64
 
-fn C.mysql_autocommit(mysql MYSQL, mode bool)
+fn C.mysql_autocommit(mysql &C.MYSQL, mode bool)
 
-fn C.mysql_refresh(mysql MYSQL, options u32) int
+fn C.mysql_refresh(mysql &C.MYSQL, options u32) int
 
-fn C.mysql_reset_connection(mysql MYSQL) int
+fn C.mysql_reset_connection(mysql &C.MYSQL) int
 
-fn C.mysql_ping(mysql MYSQL) int
+fn C.mysql_ping(mysql &C.MYSQL) int
 
 fn C.mysql_store_result(mysql &C.MYSQL) &C.MYSQL_RES
 
diff --git a/vlib/net/aasocket.c.v b/vlib/net/aasocket.c.v
index 15344a87d9..8b75e7f169 100644
--- a/vlib/net/aasocket.c.v
+++ b/vlib/net/aasocket.c.v
@@ -11,10 +11,14 @@ enum Select {
 pub enum SocketType {
 	udp = C.SOCK_DGRAM
 	tcp = C.SOCK_STREAM
+	dgram = C.SOCK_DGRAM
+	stream = C.SOCK_STREAM
+	seqpacket = C.SOCK_SEQPACKET
 }
 
 // SocketFamily are the available address families
 pub enum SocketFamily {
+	unix = C.AF_UNIX
 	inet = C.AF_INET
 }
 
@@ -55,59 +59,71 @@ mut:
 struct C.sockaddr_storage {
 }
 
-fn C.socket() int
+fn C.socket(domain SocketFamily, typ SocketType, protocol int) int
 
-fn C.setsockopt() int
+// fn C.setsockopt(sockfd int, level int, optname int, optval voidptr, optlen C.socklen_t) int
+fn C.setsockopt(sockfd int, level int, optname int, optval voidptr, optlen u32) int
 
-fn C.htonl() int
+fn C.htonl(hostlong u32) int
 
-fn C.htons() int
+fn C.htons(netshort u16) int
 
-fn C.bind() int
+// fn C.bind(sockfd int, addr &C.sockaddr, addrlen C.socklen_t) int
+// use voidptr for arg 2 becasue sockaddr is a generic descriptor for any kind of socket operation,
+// it can also take sockaddr_in depending on the type of socket used in arg 1
+fn C.bind(sockfd int, addr voidptr, addrlen u32) int
 
-fn C.listen() int
+fn C.listen(sockfd int, backlog int) int
 
-fn C.accept() int
+// fn C.accept(sockfd int, addr &C.sockaddr, addrlen &C.socklen_t) int
+fn C.accept(sockfd int, addr &C.sockaddr, addrlen &u32) int
 
-fn C.getaddrinfo() int
+fn C.getaddrinfo(node charptr, service charptr, hints &C.addrinfo, res &&C.addrinfo) int
 
-fn C.connect() int
+// fn C.connect(sockfd int, addr &C.sockaddr, addrlen C.socklen_t) int
+fn C.connect(sockfd int, addr &C.sockaddr, addrlen u32) int
 
-fn C.send() int
+// fn C.send(sockfd int, buf voidptr, len size_t, flags int) size_t
+fn C.send(sockfd int, buf voidptr, len size_t, flags int) int
 
-fn C.sendto() int
+// fn C.sendto(sockfd int, buf voidptr, len size_t, flags int, dest_add &C.sockaddr, addrlen C.socklen_t) size_t
+fn C.sendto(sockfd int, buf voidptr, len size_t, flags int, dest_add &C.sockaddr, addrlen u32) int
 
-fn C.recv() int
+// fn C.recv(sockfd int, buf voidptr, len size_t, flags int) size_t
+fn C.recv(sockfd int, buf voidptr, len size_t, flags int) int
 
-fn C.recvfrom() int
+// fn C.recvfrom(sockfd int, buf voidptr, len size_t, flags int, src_addr &C.sockaddr, addrlen &C.socklen_t) size_t
+fn C.recvfrom(sockfd int, buf voidptr, len size_t, flags int, src_addr &C.sockaddr, addrlen &u32) int
 
-fn C.shutdown() int
+fn C.shutdown(socket int, how int) int
 
-fn C.ntohs() int
+fn C.ntohs(netshort u16) int
 
-fn C.getpeername() int
+// fn C.getpeername(sockfd int, addr &C.sockaddr, addlen &C.socklen_t) int
+fn C.getpeername(sockfd int, addr &C.sockaddr, addlen &u32) int
 
-fn C.inet_ntop(af int, src voidptr, dst charptr, dst_size int) charptr
+fn C.inet_ntop(af SocketFamily, src voidptr, dst charptr, dst_size int) charptr
 
-fn C.WSAAddressToStringA() int
+fn C.WSAAddressToStringA(lpsaAddress &C.sockaddr, dwAddressLength u32, lpProtocolInfo voidptr, lpszAddressString charptr, lpdwAddressStringLength &u32) int
 
-fn C.getsockname() int
+// fn C.getsockname(sockfd int, addr &C.sockaddr, addrlen &C.socklen_t) int
+fn C.getsockname(sockfd int, addr &C.sockaddr, addrlen &u32) int
 
 // defined in builtin
 // fn C.read() int
 // fn C.close() int
 
-fn C.ioctlsocket() int
+fn C.ioctlsocket(s int, cmd int, argp &u32) int
 
-fn C.fcntl() int
+fn C.fcntl(fd int, cmd int, arg ...voidptr) int
 
-fn C.@select() int
+fn C.@select(ndfs int, readfds &C.fd_set, writefds &C.fd_set, exceptfds &C.fd_set, timeout &C.timeval) int
 
-fn C.FD_ZERO()
+fn C.FD_ZERO(fdset &C.fd_set)
 
-fn C.FD_SET()
+fn C.FD_SET(fd int, fdset &C.fd_set)
 
-fn C.FD_ISSET() bool
+fn C.FD_ISSET(fd int, fdset &C.fd_set) bool
 
 [typedef]
 pub struct C.fd_set {}
diff --git a/vlib/net/openssl/c.v b/vlib/net/openssl/c.v
index 065f4520dc..e956931a45 100644
--- a/vlib/net/openssl/c.v
+++ b/vlib/net/openssl/c.v
@@ -34,49 +34,52 @@ pub struct SSL {
 pub struct SSL_METHOD {
 }
 
-fn C.BIO_new_ssl_connect() voidptr
+fn C.BIO_new_ssl_connect(ctx &C.SSL_CTX) &C.BIO
 
-fn C.BIO_set_conn_hostname() int
+fn C.BIO_set_conn_hostname(b &C.BIO, name charptr) int
 
-fn C.BIO_get_ssl()
+// there are actually 2 macros for BIO_get_ssl
+// fn C.BIO_get_ssl(bp &C.BIO, ssl charptr, c int)
+// fn C.BIO_get_ssl(bp &C.BIO, sslp charptr)
+fn C.BIO_get_ssl(bp &C.BIO, vargs ...voidptr)
 
-fn C.BIO_do_connect() int
+fn C.BIO_do_connect(b &C.BIO) int
 
-fn C.BIO_do_handshake() int
+fn C.BIO_do_handshake(b &C.BIO) int
 
-fn C.BIO_puts()
+fn C.BIO_puts(b &C.BIO, buf charptr)
 
-fn C.BIO_read() int
+fn C.BIO_read(b &C.BIO, buf voidptr, len int) int
 
-fn C.BIO_free_all()
+fn C.BIO_free_all(a &C.BIO)
 
-fn C.SSL_CTX_new() &C.SSL_CTX
+fn C.SSL_CTX_new(method &C.SSL_METHOD) &C.SSL_CTX
 
-fn C.SSL_CTX_set_options()
+fn C.SSL_CTX_set_options(ctx &C.SSL_CTX, options int)
 
-fn C.SSL_CTX_set_verify_depth()
+fn C.SSL_CTX_set_verify_depth(s &C.SSL_CTX, depth int)
 
-fn C.SSL_CTX_load_verify_locations() int
+fn C.SSL_CTX_load_verify_locations(ctx &C.SSL_CTX, ca_file charptr, ca_path charptr) int
 
-fn C.SSL_CTX_free()
+fn C.SSL_CTX_free(ctx &C.SSL_CTX)
 
 fn C.SSL_new(&C.SSL_CTX) &C.SSL
 
-fn C.SSL_set_fd(&C.SSL) int
+fn C.SSL_set_fd(ssl &C.SSL, fd int) int
 
 fn C.SSL_connect(&C.SSL) int
 
-fn C.SSL_set_cipher_list() int
+fn C.SSL_set_cipher_list(ctx &SSL, str charptr) int
 
-fn C.SSL_get_peer_certificate() int
+fn C.SSL_get_peer_certificate(ssl &SSL) &C.X509
 
 fn C.ERR_clear_error()
 
-fn C.SSL_get_error() int
+fn C.SSL_get_error(ssl &C.SSL, ret int) int
 
-fn C.SSL_get_verify_result() int
+fn C.SSL_get_verify_result(ssl &SSL) int
 
-fn C.SSL_set_tlsext_host_name() int
+fn C.SSL_set_tlsext_host_name(s &SSL, name charptr) int
 
 fn C.SSL_shutdown(&C.SSL) int
 
diff --git a/vlib/net/tcp.v b/vlib/net/tcp.v
index 3bb62e988e..902443af0e 100644
--- a/vlib/net/tcp.v
+++ b/vlib/net/tcp.v
@@ -157,7 +157,7 @@ pub fn (c &TcpConn) peer_ip() ?string {
 	peeraddr := C.sockaddr_in{}
 	speeraddr := sizeof(peeraddr)
 	socket_error(C.getpeername(c.sock.handle, unsafe { &C.sockaddr(&peeraddr) }, &speeraddr)) ?
-	cstr := charptr(C.inet_ntop(C.AF_INET, &peeraddr.sin_addr, buf, sizeof(buf)))
+	cstr := charptr(C.inet_ntop(SocketFamily.inet, &peeraddr.sin_addr, buf, sizeof(buf)))
 	if cstr == 0 {
 		return error('net.peer_ip: inet_ntop failed')
 	}
@@ -264,7 +264,7 @@ fn new_tcp_socket() ?TcpSocket {
 	// s.set_option_bool(.reuse_addr, true)?
 	s.set_option_int(.reuse_addr, 1) ?
 	$if windows {
-		t := true
+		t := u32(1) // true
 		socket_error(C.ioctlsocket(sockfd, fionbio, &t)) ?
 	} $else {
 		socket_error(C.fcntl(sockfd, C.F_SETFL, C.fcntl(sockfd, C.F_GETFL) | C.O_NONBLOCK)) ?
@@ -279,7 +279,7 @@ fn tcp_socket_from_handle(sockfd int) ?TcpSocket {
 	// s.set_option_bool(.reuse_addr, true)?
 	s.set_option_int(.reuse_addr, 1) ?
 	$if windows {
-		t := true
+		t := u32(1) // true
 		socket_error(C.ioctlsocket(sockfd, fionbio, &t)) ?
 	} $else {
 		socket_error(C.fcntl(sockfd, C.F_SETFL, C.fcntl(sockfd, C.F_GETFL) | C.O_NONBLOCK)) ?
diff --git a/vlib/net/udp.v b/vlib/net/udp.v
index fac1320d59..8f674445f7 100644
--- a/vlib/net/udp.v
+++ b/vlib/net/udp.v
@@ -181,7 +181,7 @@ fn new_udp_socket(local_port int) ?&UdpSocket {
 	}
 	s.set_option_bool(.reuse_addr, true) ?
 	$if windows {
-		t := true
+		t := u32(1) // true
 		socket_error(C.ioctlsocket(sockfd, fionbio, &t)) ?
 	} $else {
 		socket_error(C.fcntl(sockfd, C.F_SETFD, C.O_NONBLOCK)) ?
diff --git a/vlib/net/unix/aasocket.c.v b/vlib/net/unix/aasocket.c.v
index a40639e54a..25abb47066 100644
--- a/vlib/net/unix/aasocket.c.v
+++ b/vlib/net/unix/aasocket.c.v
@@ -8,11 +8,11 @@ enum Select {
 }
 
 // SocketType are the available sockets
-enum SocketType {
-	dgram = C.SOCK_DGRAM
-	stream = C.SOCK_STREAM
-	seqpacket = C.SOCK_SEQPACKET
-}
+// enum SocketType {
+// 	dgram = C.SOCK_DGRAM
+// 	stream = C.SOCK_STREAM
+// 	seqpacket = C.SOCK_SEQPACKET
+// }
 
 struct C.sockaddr {
 	sa_family u16
@@ -44,43 +44,43 @@ mut:
 struct C.sockaddr_storage {
 }
 
-fn C.socket() int
+// fn C.socket() int
 
-fn C.setsockopt() int
+// fn C.setsockopt() int
 
-fn C.htonl() int
+// fn C.htonl() int
 
-fn C.htons() int
+// fn C.htons() int
 
-fn C.bind() int
+// fn C.bind() int
 
-fn C.listen() int
+// fn C.listen() int
 
-fn C.accept() int
+// fn C.accept() int
 
-fn C.getaddrinfo() int
+// fn C.getaddrinfo() int
 
-fn C.connect() int
+// fn C.connect() int
 
-fn C.send() int
+// fn C.send() int
 
-fn C.sendto() int
+// fn C.sendto() int
 
-fn C.recv() int
+// fn C.recv() int
 
-fn C.recvfrom() int
+// fn C.recvfrom() int
 
-fn C.shutdown() int
+// fn C.shutdown() int
 
-fn C.ntohs() int
+// fn C.ntohs() int
 
-fn C.getpeername() int
+// fn C.getpeername() int
 
-fn C.inet_ntop(af int, src voidptr, dst charptr, dst_size int) charptr
+// fn C.inet_ntop(af int, src voidptr, dst charptr, dst_size int) charptr
 
 fn C.WSAAddressToStringA() int
 
-fn C.getsockname() int
+// fn C.getsockname() int
 
 // defined in builtin
 // fn C.read() int
@@ -88,15 +88,15 @@ fn C.getsockname() int
 
 fn C.ioctlsocket() int
 
-fn C.fcntl() int
+// fn C.fcntl() int
 
-fn C.@select() int
+// fn C.@select() int
 
-fn C.FD_ZERO()
+// fn C.FD_ZERO()
 
-fn C.FD_SET()
+// fn C.FD_SET()
 
-fn C.FD_ISSET() bool
+// fn C.FD_ISSET() bool
 
 [typedef]
 struct C.fd_set {}
diff --git a/vlib/net/unix/common.v b/vlib/net/unix/common.v
index c2779a5cb8..c44d9973d1 100644
--- a/vlib/net/unix/common.v
+++ b/vlib/net/unix/common.v
@@ -7,7 +7,7 @@ const (
 	error_ewouldblock = C.EWOULDBLOCK
 )
 
-fn C.SUN_LEN(C.sockaddr_un) int
+fn C.SUN_LEN(ptr &C.sockaddr_un) int
 
 fn C.strncpy(charptr, charptr, int)
 
diff --git a/vlib/net/unix/stream_nix.v b/vlib/net/unix/stream_nix.v
index 120d689851..0a23ed8bca 100644
--- a/vlib/net/unix/stream_nix.v
+++ b/vlib/net/unix/stream_nix.v
@@ -41,7 +41,7 @@ fn error_code() int {
 }
 
 fn new_stream_socket() ?StreamSocket {
-	sockfd := net.socket_error(C.socket(C.AF_UNIX, SocketType.stream, 0)) ?
+	sockfd := net.socket_error(C.socket(net.SocketFamily.unix, net.SocketType.stream, 0)) ?
 	mut s := StreamSocket{
 		handle: sockfd
 	}
diff --git a/vlib/os/os_c.v b/vlib/os/os_c.v
index 8ed3e98dac..250cffdf7b 100644
--- a/vlib/os/os_c.v
+++ b/vlib/os/os_c.v
@@ -9,7 +9,7 @@ struct C.dirent {
 
 fn C.readdir(voidptr) &C.dirent
 
-fn C.readlink() int
+fn C.readlink(pathname charptr, buf charptr, bufsiz size_t) int
 
 fn C.getline(voidptr, voidptr, voidptr) int
 
@@ -19,7 +19,7 @@ fn C.sigaction(int, voidptr, int)
 
 fn C.open(charptr, int, ...int) int
 
-fn C.fdopen(int, string) voidptr
+fn C.fdopen(fd int, mode charptr) &C.FILE
 
 fn C.CopyFile(&u32, &u32, int) int
 
@@ -408,8 +408,7 @@ pub fn get_raw_line() string {
 			h_input := C.GetStdHandle(C.STD_INPUT_HANDLE)
 			mut bytes_read := 0
 			if is_atty(0) > 0 {
-				x := C.ReadConsole(h_input, buf, max_line_chars * 2, C.LPDWORD(&bytes_read),
-					0)
+				x := C.ReadConsole(h_input, buf, max_line_chars * 2, &bytes_read, 0)
 				if !x {
 					return tos(buf, 0)
 				}
diff --git a/vlib/picoev/picoev.v b/vlib/picoev/picoev.v
index 6b7825dbd2..58678d69fc 100644
--- a/vlib/picoev/picoev.v
+++ b/vlib/picoev/picoev.v
@@ -40,39 +40,48 @@ struct C.sockaddr_storage {
 
 fn C.atoi() int
 
-fn C.strncasecmp() int
+fn C.strncasecmp(s1 charptr, s2 charptr, n size_t) int
 
-fn C.socket() int
+fn C.socket(domain int, typ int, protocol int) int
 
-fn C.setsockopt() int
+// fn C.setsockopt(sockfd int, level int, optname int, optval voidptr, optlen C.socklen_t) int
+fn C.setsockopt(sockfd int, level int, optname int, optval voidptr, optlen u32) int
 
-fn C.htonl() int
+fn C.htonl(hostlong u32) int
 
-fn C.htons() int
+fn C.htons(netshort u16) int
 
-fn C.bind() int
+// fn C.bind(sockfd int, addr &C.sockaddr, addrlen C.socklen_t) int
+// use voidptr for arg 2 becasue sockaddr is a generic descriptor for any kind of socket operation,
+// it can also take sockaddr_in depending on the type of socket used in arg 1
+fn C.bind(sockfd int, addr voidptr, addrlen u32) int
 
-fn C.listen() int
+fn C.listen(sockfd int, backlog int) int
 
-fn C.accept() int
+// fn C.accept(sockfd int, addr &C.sockaddr, addrlen &C.socklen_t) int
+fn C.accept(sockfd int, addr &C.sockaddr, addrlen &u32) int
 
-fn C.getaddrinfo() int
+fn C.getaddrinfo(node charptr, service charptr, hints &C.addrinfo, res &&C.addrinfo) int
 
-fn C.connect() int
+// fn C.connect(sockfd int, addr &C.sockaddr, addrlen C.socklen_t) int
+fn C.connect(sockfd int, addr &C.sockaddr, addrlen u32) int
 
-fn C.send() int
+// fn C.send(sockfd int, buf voidptr, len size_t, flags int) size_t
+fn C.send(sockfd int, buf voidptr, len size_t, flags int) int
 
-fn C.recv() int
+// fn C.recv(sockfd int, buf voidptr, len size_t, flags int) size_t
+fn C.recv(sockfd int, buf voidptr, len size_t, flags int) int
 
 // fn C.read() int
-fn C.shutdown() int
+fn C.shutdown(socket int, how int) int
 
 // fn C.close() int
-fn C.ntohs() int
+fn C.ntohs(netshort u16) int
 
-fn C.getsockname() int
+// fn C.getsockname(sockfd int, addr &C.sockaddr, addrlen &C.socklen_t) int
+fn C.getsockname(sockfd int, addr &C.sockaddr, addrlen &u32) int
 
-fn C.fcntl() int
+fn C.fcntl(fd int, cmd int, arg ...voidptr) int
 
 // fn C.write() int
 struct C.picoev_loop {
@@ -93,7 +102,11 @@ fn C.picoev_del(&C.picoev_loop, int) int
 
 fn C.picoev_set_timeout(&C.picoev_loop, int, int)
 
-fn C.picoev_add(&C.picoev_loop, int, int, int, &C.picoev_handler, voidptr) int
+// fn C.picoev_handler(loop &C.picoev_loop, fd int, revents int, cb_arg voidptr)
+// TODO: (sponge) update to C.picoev_handler with C type def update
+type Cpicoev_handler = fn(loop &C.picoev_loop, fd int, revents int, cb_arg voidptr)
+
+fn C.picoev_add(&C.picoev_loop, int, int, int, &Cpicoev_handler, voidptr) int
 
 fn C.picoev_init(int) int
 
@@ -105,12 +118,6 @@ fn C.picoev_destroy_loop(&C.picoev_loop) int
 
 fn C.picoev_deinit() int
 
-fn C.phr_parse_request() int
-
-fn C.phr_parse_request_path_pipeline() int
-
-fn C.phr_parse_request_path() int
-
 [inline]
 fn setup_sock(fd int) {
 	on := 1
diff --git a/vlib/picohttpparser/picohttpparser.v b/vlib/picohttpparser/picohttpparser.v
index 98182aff1c..1dc9b31fcf 100644
--- a/vlib/picohttpparser/picohttpparser.v
+++ b/vlib/picohttpparser/picohttpparser.v
@@ -11,18 +11,22 @@ module picohttpparser
 
 struct C.phr_header {
 pub:
-	name charptr
-	name_len int
-	value charptr
+	name      charptr
+	name_len  int
+	value     charptr
 	value_len int
 }
+
 struct C.phr_header_t {}
 
-fn C.phr_parse_request() int
-fn C.phr_parse_response() int
-fn C.phr_parse_headers() int
+fn C.phr_parse_request(buf charptr, len size_t, method &charptr, method_len &size_t, path &charptr, path_len &size_t, minor_version &int, headers &C.phr_header, num_headers &size_t, last_len size_t) int
 
-fn C.phr_parse_request_path() int
-fn C.phr_parse_request_path_pipeline() int
+fn C.phr_parse_response(buf charptr, len size_t, minor_version &int, status &int, msg &charptr, msg_len &size_t, headers &C.phr_header, num_headers &size_t, last_len size_t) int
+
+fn C.phr_parse_headers(buf charptr, len size_t, headers &C.phr_header, num_headers &size_t, last_len size_t) int
+
+fn C.phr_parse_request_path(buf_start charptr, len size_t, method &charptr, method_len &size_t, path &charptr, path_len &size_t) int
+fn C.phr_parse_request_path_pipeline(buf_start charptr, len size_t, method &charptr, method_len &size_t, path &charptr, path_len &size_t) int
 fn C.get_date() byteptr
-fn C.u64toa() int
+// char * u64toa(uint64_t value, char *buffer)
+fn C.u64toa(value u64, buffer charptr) charptr
diff --git a/vlib/picohttpparser/request.v b/vlib/picohttpparser/request.v
index 573cfd3076..60ba3125c1 100644
--- a/vlib/picohttpparser/request.v
+++ b/vlib/picohttpparser/request.v
@@ -21,8 +21,8 @@ pub fn (mut r Request) parse_request(s string, max_headers int) int {
 
 	pret := C.phr_parse_request(
 		s.str, s.len,
-		&r.method, &method_len,
-		&r.path, &path_len,
+		&r.method.str, &method_len,
+		&r.path.str, &path_len,
 		&minor_version,
 		r.headers, &num_headers,
 		0
@@ -44,8 +44,8 @@ pub fn (mut r Request) parse_request_path(s string) int {
 
 	pret := C.phr_parse_request_path(
 		s.str, s.len,
-		&r.method, &method_len,
-		&r.path, &path_len
+		&r.method.str, &method_len,
+		&r.path.str, &path_len
 	)
 	if pret > 0 {
 		unsafe {
@@ -63,8 +63,8 @@ pub fn (mut r Request) parse_request_path_pipeline(s string) int {
 
 	pret := C.phr_parse_request_path_pipeline(
 		s.str, s.len,
-		&r.method, &method_len,
-		&r.path, &path_len
+		&r.method.str, &method_len,
+		&r.path.str, &path_len
 	)
 	if pret > 0 {
 		unsafe {
diff --git a/vlib/readline/readline_linux.c.v b/vlib/readline/readline_linux.c.v
index ad195e5f9f..3dd521181d 100644
--- a/vlib/readline/readline_linux.c.v
+++ b/vlib/readline/readline_linux.c.v
@@ -12,11 +12,11 @@ import os
 
 #include <termios.h>
 #include <sys/ioctl.h>
-fn C.tcgetattr() int
+fn C.tcgetattr(fd int, termios_p &Termios) int
 
-fn C.tcsetattr() int
+fn C.tcsetattr(fd int, optional_actions int, termios_p &Termios) int
 
-fn C.raise()
+fn C.raise(sig int)
 
 fn C.getppid() int
 
diff --git a/vlib/sokol/sfons/sfons_funcs.v b/vlib/sokol/sfons/sfons_funcs.v
index ea49749a22..cec30d688f 100644
--- a/vlib/sokol/sfons/sfons_funcs.v
+++ b/vlib/sokol/sfons/sfons_funcs.v
@@ -1,6 +1,6 @@
 module sfons
 
 fn C.sfons_create(width int, height int, flags int) &C.FONScontext
-fn C.sfons_destroy(ctx &FONScontext)
+fn C.sfons_destroy(ctx &C.FONScontext)
 fn C.sfons_rgba(r byte, g byte, b byte, a byte) u32
-fn C.sfons_flush(ctx &FONScontext)
+fn C.sfons_flush(ctx &C.FONScontext)
diff --git a/vlib/sqlite/sqlite.v b/vlib/sqlite/sqlite.v
index 4902e852e7..ccc9638b54 100644
--- a/vlib/sqlite/sqlite.v
+++ b/vlib/sqlite/sqlite.v
@@ -41,7 +41,7 @@ fn C.sqlite3_open(charptr, &&C.sqlite3) int
 fn C.sqlite3_close(&C.sqlite3) int
 
 //
-fn C.sqlite3_prepare_v2(&C.sqlite3, charptr, int, &&sqlite3_stmt, &charptr) int
+fn C.sqlite3_prepare_v2(&C.sqlite3, charptr, int, &&C.sqlite3_stmt, &charptr) int
 
 fn C.sqlite3_step(&C.sqlite3_stmt) int
 
diff --git a/vlib/term/term_nix.c.v b/vlib/term/term_nix.c.v
index 837cdede33..6dab16ae4c 100644
--- a/vlib/term/term_nix.c.v
+++ b/vlib/term/term_nix.c.v
@@ -4,6 +4,7 @@ import os
 
 #include <sys/ioctl.h>
 #include <termios.h> // TIOCGWINSZ
+
 pub struct C.winsize {
 pub:
 	ws_row    u16
@@ -20,7 +21,7 @@ pub fn get_terminal_size() (int, int) {
 		return default_columns_size, default_rows_size
 	}
 	w := C.winsize{}
-	C.ioctl(1, C.TIOCGWINSZ, &w)
+	C.ioctl(1, u64(C.TIOCGWINSZ), &w)
 	return int(w.ws_col), int(w.ws_row)
 }
 
@@ -52,7 +53,7 @@ pub fn get_cursor_position() Coord {
 		i++
 		if i >= 15 {
 			panic('C.getchar() called too many times')
-		}        
+		}
 		// state management:
 		if b == `R` {
 			break
diff --git a/vlib/term/term_windows.c.v b/vlib/term/term_windows.c.v
index bd579f72d0..74d259de08 100644
--- a/vlib/term/term_windows.c.v
+++ b/vlib/term/term_windows.c.v
@@ -44,16 +44,16 @@ mut:
 }
 
 // ref - https://docs.microsoft.com/en-us/windows/console/getconsolescreenbufferinfo
-fn C.GetConsoleScreenBufferInfo(handle os.HANDLE, info &C.CONSOLE_SCREEN_BUFFER_INFO) bool
+fn C.GetConsoleScreenBufferInfo(handle C.HANDLE, info &C.CONSOLE_SCREEN_BUFFER_INFO) bool
 
 // ref - https://docs.microsoft.com/en-us/windows/console/setconsoletitle
 fn C.SetConsoleTitle(title &u16) bool
 
 // ref - https://docs.microsoft.com/en-us/windows/console/setconsolecursorposition
-fn C.SetConsoleCursorPosition(handle os.HANDLE, coord C.COORD) bool
+fn C.SetConsoleCursorPosition(handle C.HANDLE, coord C.COORD) bool
 
 // ref - https://docs.microsoft.com/en-us/windows/console/scrollconsolescreenbuffer
-fn C.ScrollConsoleScreenBuffer(output os.HANDLE, scroll_rect &C.SMALL_RECT, clip_rect &C.SMALL_RECT, des C.COORD, fill C.CHAR_INFO) bool
+fn C.ScrollConsoleScreenBuffer(output C.HANDLE, scroll_rect &C.SMALL_RECT, clip_rect &C.SMALL_RECT, des C.COORD, fill &C.CHAR_INFO) bool
 
 // get_terminal_size returns a number of colums and rows of terminal window.
 pub fn get_terminal_size() (int, int) {
diff --git a/vlib/term/ui/consoleapi_windows.c.v b/vlib/term/ui/consoleapi_windows.c.v
index 19d521a0d0..96b3cc4017 100644
--- a/vlib/term/ui/consoleapi_windows.c.v
+++ b/vlib/term/ui/consoleapi_windows.c.v
@@ -77,8 +77,8 @@ struct C.CONSOLE_SCREEN_BUFFER_INFO {
 	dwMaximumWindowSize C.COORD
 }
 
-fn C.ReadConsoleInput() bool
+fn C.ReadConsoleInput(hConsoleInput C.HANDLE, lpBuffer &C.INPUT_RECORD, nLength u32, lpNumberOfEventsRead &u32) bool
 
-fn C.GetNumberOfConsoleInputEvents() bool
+fn C.GetNumberOfConsoleInputEvents(hConsoleInput C.HANDLE, lpcNumberOfEvents &u32) bool
 
-fn C.GetConsoleScreenBufferInfo(handle os.HANDLE, info &C.CONSOLE_SCREEN_BUFFER_INFO) bool
+fn C.GetConsoleScreenBufferInfo(handle C.HANDLE, info &C.CONSOLE_SCREEN_BUFFER_INFO) bool
diff --git a/vlib/term/ui/termios_nix.c.v b/vlib/term/ui/termios_nix.c.v
index 4672125977..6a338281ca 100644
--- a/vlib/term/ui/termios_nix.c.v
+++ b/vlib/term/ui/termios_nix.c.v
@@ -10,9 +10,9 @@ import time
 #include <sys/ioctl.h>
 #include <signal.h>
 
-fn C.tcgetattr()
+fn C.tcgetattr(fd int, termios_p &C.termios) int
 
-fn C.tcsetattr()
+fn C.tcsetattr(fd int, optional_actions int, termios_p &C.termios) int
 
 fn C.ioctl(fd int, request u64, arg voidptr) int
 
diff --git a/vlib/time/time_nix.c.v b/vlib/time/time_nix.c.v
index 47a17f60dc..79f06c884c 100644
--- a/vlib/time/time_nix.c.v
+++ b/vlib/time/time_nix.c.v
@@ -17,10 +17,10 @@ struct C.tm {
 	tm_isdst int
 }
 
-fn C.timegm(&tm) time_t
+fn C.timegm(&C.tm) time_t
 
 // fn C.gmtime_r(&tm, &gbuf)
-fn C.localtime_r(t &C.time_t, tm &C.tm)
+fn C.localtime_r(t &time_t, tm &C.tm)
 
 fn make_unix_time(t C.tm) int {
 	return int(C.timegm(&t))
diff --git a/vlib/time/time_windows.c.v b/vlib/time/time_windows.c.v
index 1aa9bef937..974416b161 100644
--- a/vlib/time/time_windows.c.v
+++ b/vlib/time/time_windows.c.v
@@ -29,11 +29,11 @@ struct SystemTime {
 	millisecond u16
 }
 
-fn C.GetSystemTimeAsFileTime(lpSystemTimeAsFileTime C._FILETIME)
+fn C.GetSystemTimeAsFileTime(lpSystemTimeAsFileTime &C._FILETIME)
 
-fn C.FileTimeToSystemTime()
+fn C.FileTimeToSystemTime(lpFileTime &C._FILETIME, lpSystemTime &SystemTime)
 
-fn C.SystemTimeToTzSpecificLocalTime()
+fn C.SystemTimeToTzSpecificLocalTime(lpTimeZoneInformation &C.TIME_ZONE_INFORMATION, lpUniversalTime &SystemTime, lpLocalTime &SystemTime)
 
 fn C.localtime_s(t &C.time_t, tm &C.tm)
 
diff --git a/vlib/v/checker/check_types.v b/vlib/v/checker/check_types.v
index 7ad0b96345..13e2857bd5 100644
--- a/vlib/v/checker/check_types.v
+++ b/vlib/v/checker/check_types.v
@@ -7,7 +7,7 @@ import v.table
 import v.token
 import v.ast
 
-pub fn (mut c Checker) check_expected_call_arg(got table.Type, expected_ table.Type) ? {
+pub fn (mut c Checker) check_expected_call_arg(got table.Type, expected_ table.Type, language table.Language) ? {
 	mut expected := expected_
 	// variadic
 	if expected.has_flag(.variadic) {
@@ -15,6 +15,39 @@ pub fn (mut c Checker) check_expected_call_arg(got table.Type, expected_ table.T
 		exp_info := exp_type_sym.info as table.Array
 		expected = exp_info.elem_type
 	}
+	if language == .c {
+		// allow number types to be used interchangeably
+		if got.is_number() && expected.is_number() {
+			return
+		}
+		// mode_t - currently using u32 as mode_t for C fns
+		// if got.idx() in [table.int_type_idx, table.u32_type_idx] && expected.idx() in [table.int_type_idx, table.u32_type_idx] {
+		// 	return
+		// }
+		// allow number to be used as size_t
+		if got.is_number() && expected.idx() == table.size_t_type_idx {
+			return
+		}
+		// allow bool & int to be used interchangeably for C functions
+		if (got.idx() == table.bool_type_idx
+			&& expected.idx() in [table.int_type_idx, table.int_literal_type_idx])
+			|| (expected.idx() == table.bool_type_idx
+			&& got.idx() in [table.int_type_idx, table.int_literal_type_idx]) {
+			return
+		}
+		if got.idx() == table.string_type_idx
+			&& expected in [table.byteptr_type_idx, table.charptr_type_idx] {
+			return
+		}
+		exp_sym := c.table.get_type_symbol(expected)
+		// unknown C types are set to int, allow int to be used for types like `&C.FILE`
+		// eg. `C.fflush(C.stderr)` - error: cannot use `int` as `&C.FILE` in argument 1 to `C.fflush`
+		if expected.is_ptr() && exp_sym.language == .c && exp_sym.kind == .placeholder
+			&& got == table.int_type_idx {
+			return
+		}
+		// return
+	}
 	if c.check_types(got, expected) {
 		return
 	}
@@ -46,6 +79,17 @@ pub fn (mut c Checker) check_basic(got table.Type, expected table.Type) bool {
 			return true
 		}
 	}
+	// e.g. [4096]byte vs byteptr || [4096]char vs charptr
+	// should charptr be allowed as byteptr etc?
+	// TODO: clean this up (why was it removed?)
+	if got_sym.kind == .array_fixed {
+		info := got_sym.info as table.ArrayFixed
+		if !info.elem_type.is_ptr() && (info.elem_type.idx() == expected.idx()
+			|| (info.elem_type.idx() in [table.byte_type_idx, table.char_type_idx]
+			&& expected.idx() in [table.byteptr_type_idx, table.charptr_type_idx])) {
+			return true
+		}
+	}
 	if exp_sym.kind in [.voidptr, .any] || got_sym.kind in [.voidptr, .any] {
 		return true
 	}
@@ -157,7 +201,7 @@ fn (c &Checker) promote_num(left_type table.Type, right_type table.Type) table.T
 	}
 	idx_hi := type_hi.idx()
 	idx_lo := type_lo.idx()
-	// the following comparisons rely on the order of the indices in atypes.v
+	// the following comparisons rely on the order of the indices in table/types.v
 	if idx_hi == table.int_literal_type_idx {
 		return type_lo
 	} else if idx_hi == table.float_literal_type_idx {
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 5656c94e1d..3d574124f8 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -1546,7 +1546,7 @@ pub fn (mut c Checker) call_method(mut call_expr ast.CallExpr) table.Type {
 			if method.generic_names.len > 0 {
 				continue
 			}
-			c.check_expected_call_arg(got_arg_typ, exp_arg_typ) or {
+			c.check_expected_call_arg(got_arg_typ, exp_arg_typ, call_expr.language) or {
 				// str method, allow type with str method if fn arg is string
 				// Passing an int or a string array produces a c error here
 				// Deleting this condition results in propper V error messages
@@ -1866,32 +1866,19 @@ pub fn (mut c Checker) call_fn(mut call_expr ast.CallExpr) table.Type {
 		&& f.ctdefine !in c.pref.compile_defines {
 		call_expr.should_be_skipped = true
 	}
-	if f.language != .v || call_expr.language != .v {
-		// ignore C function of type `fn()`, assume untyped
-		// For now don't check C functions that are variadic, underscored, capitalized
-		// or have no params or attributes and return int
-		if f.language == .c && f.params.len != call_expr.args.len && !f.is_variadic
-			&& f.name[2] != `_` && !f.name[2].is_capital() && (f.params.len != 0
-			|| f.return_type !in [table.void_type, table.int_type]
-			|| f.attrs.len > 0) {
-			// change to error later
-			c.warn('expected $f.params.len arguments, but got $call_expr.args.len', call_expr.pos)
+	// dont check number of args for JS functions since arguments are not required 
+	if call_expr.language != .js {
+		min_required_args := if f.is_variadic { f.params.len - 1 } else { f.params.len }
+		if call_expr.args.len < min_required_args {
+			c.error('expected $min_required_args arguments, but got $call_expr.args.len',
+				call_expr.pos)
+		} else if !f.is_variadic && call_expr.args.len > f.params.len {
+			unexpected_arguments := call_expr.args[min_required_args..]
+			unexpected_arguments_pos := unexpected_arguments[0].pos.extend(unexpected_arguments.last().pos)
+			c.error('expected $min_required_args arguments, but got $call_expr.args.len',
+				unexpected_arguments_pos)
+			return f.return_type
 		}
-		for arg in call_expr.args {
-			c.expr(arg.expr)
-		}
-		return f.return_type
-	}
-	min_required_args := if f.is_variadic { f.params.len - 1 } else { f.params.len }
-	if call_expr.args.len < min_required_args {
-		c.error('expected $min_required_args arguments, but got $call_expr.args.len',
-			call_expr.pos)
-	} else if !f.is_variadic && call_expr.args.len > f.params.len {
-		unexpected_arguments := call_expr.args[min_required_args..]
-		unexpected_arguments_pos := unexpected_arguments[0].pos.extend(unexpected_arguments.last().pos)
-		c.error('expected $min_required_args arguments, but got $call_expr.args.len',
-			unexpected_arguments_pos)
-		return f.return_type
 	}
 	// println / eprintln / panic can print anything
 	if fn_name in ['println', 'print', 'eprintln', 'eprint', 'panic'] && call_expr.args.len > 0 {
@@ -1960,7 +1947,7 @@ pub fn (mut c Checker) call_fn(mut call_expr ast.CallExpr) table.Type {
 			c.error('function with `shared` arguments cannot be called inside `lock`/`rlock` block',
 				call_arg.pos)
 		}
-		if call_arg.is_mut {
+		if call_arg.is_mut && f.language == .v {
 			to_lock, pos := c.fail_if_immutable(call_arg.expr)
 			if !arg.is_mut {
 				tok := call_arg.share.str()
@@ -1991,7 +1978,7 @@ pub fn (mut c Checker) call_fn(mut call_expr ast.CallExpr) table.Type {
 			c.type_implements(typ, arg.typ, call_arg.expr.position())
 			continue
 		}
-		c.check_expected_call_arg(typ, arg.typ) or {
+		c.check_expected_call_arg(typ, arg.typ, call_expr.language) or {
 			// str method, allow type with str method if fn arg is string
 			// Passing an int or a string array produces a c error here
 			// Deleting this condition results in propper V error messages
diff --git a/vlib/v/checker/tests/c_fn_surplus_args.out b/vlib/v/checker/tests/c_fn_surplus_args.out
index 9f470d920d..a462c8470d 100644
--- a/vlib/v/checker/tests/c_fn_surplus_args.out
+++ b/vlib/v/checker/tests/c_fn_surplus_args.out
@@ -1,3 +1,10 @@
+vlib/v/checker/tests/c_fn_surplus_args.vv:6:7: error: expected 0 arguments, but got 1
+    4 | 
+    5 | fn main() {
+    6 |     C.no(1) // allowed
+      |          ^
+    7 |     C.y1()
+    8 |     C.y1(1) // ok
 vlib/v/checker/tests/c_fn_surplus_args.vv:7:4: error: expected 1 arguments, but got 0
     5 | fn main() {
     6 |     C.no(1) // allowed
@@ -5,18 +12,18 @@ vlib/v/checker/tests/c_fn_surplus_args.vv:7:4: error: expected 1 arguments, but
       |       ~~~~
     8 |     C.y1(1) // ok
     9 |     C.y1(1, 2)
-vlib/v/checker/tests/c_fn_surplus_args.vv:9:4: error: expected 1 arguments, but got 2
+vlib/v/checker/tests/c_fn_surplus_args.vv:9:10: error: expected 1 arguments, but got 2
     7 |     C.y1()
     8 |     C.y1(1) // ok
     9 |     C.y1(1, 2)
-      |       ~~~~~~~~
+      |             ^
    10 |     C.ret() // ok
    11 |     C.ret(1)
-vlib/v/checker/tests/c_fn_surplus_args.vv:11:4: error: expected 0 arguments, but got 1
+vlib/v/checker/tests/c_fn_surplus_args.vv:11:8: error: expected 0 arguments, but got 1
     9 |     C.y1(1, 2)
    10 |     C.ret() // ok
    11 |     C.ret(1)
-      |       ~~~~~~
+      |           ^
    12 |     // avoid cgen whilst warning, later above should error
    13 |     main()
 vlib/v/checker/tests/c_fn_surplus_args.vv:13:2: error: the `main` function cannot be called in the program
@@ -26,10 +33,10 @@ vlib/v/checker/tests/c_fn_surplus_args.vv:13:2: error: the `main` function canno
       |     ~~~~~~
    14 |     C.af() // ok
    15 |     C.af(3)
-vlib/v/checker/tests/c_fn_surplus_args.vv:15:4: error: expected 0 arguments, but got 1
+vlib/v/checker/tests/c_fn_surplus_args.vv:15:7: error: expected 0 arguments, but got 1
    13 |     main()
    14 |     C.af() // ok
    15 |     C.af(3)
-      |       ~~~~~
+      |          ^
    16 | }
    17 |
diff --git a/vlib/v/gen/c/fn.v b/vlib/v/gen/c/fn.v
index b644621d26..8241c159da 100644
--- a/vlib/v/gen/c/fn.v
+++ b/vlib/v/gen/c/fn.v
@@ -1000,8 +1000,9 @@ fn (mut g Gen) autofree_call_postgen(node_pos int) {
 fn (mut g Gen) call_args(node ast.CallExpr) {
 	args := if g.is_js_call { node.args[1..] } else { node.args }
 	expected_types := node.expected_arg_types
+	// only v variadic, C variadic args will be appeneded like normal args
 	is_variadic := expected_types.len > 0
-		&& expected_types[expected_types.len - 1].has_flag(.variadic)
+		&& expected_types[expected_types.len - 1].has_flag(.variadic) && node.language == .v
 	for i, arg in args {
 		if is_variadic && i == expected_types.len - 1 {
 			break
@@ -1024,7 +1025,7 @@ fn (mut g Gen) call_args(node ast.CallExpr) {
 					g.write('/*af arg*/' + name)
 				}
 			} else {
-				g.ref_or_deref_arg(arg, expected_types[i])
+				g.ref_or_deref_arg(arg, expected_types[i], node.language)
 			}
 		} else {
 			if use_tmp_var_autofree {
@@ -1054,7 +1055,7 @@ fn (mut g Gen) call_args(node ast.CallExpr) {
 			if variadic_count > 0 {
 				g.write('new_array_from_c_array($variadic_count, $variadic_count, sizeof($elem_type), _MOV(($elem_type[$variadic_count]){')
 				for j in arg_nr .. args.len {
-					g.ref_or_deref_arg(args[j], arr_info.elem_type)
+					g.ref_or_deref_arg(args[j], arr_info.elem_type, node.language)
 					if j < args.len - 1 {
 						g.write(', ')
 					}
@@ -1068,7 +1069,7 @@ fn (mut g Gen) call_args(node ast.CallExpr) {
 }
 
 [inline]
-fn (mut g Gen) ref_or_deref_arg(arg ast.CallArg, expected_type table.Type) {
+fn (mut g Gen) ref_or_deref_arg(arg ast.CallArg, expected_type table.Type, lang table.Language) {
 	arg_is_ptr := expected_type.is_ptr() || expected_type.idx() in table.pointer_type_idxs
 	expr_is_ptr := arg.typ.is_ptr() || arg.typ.idx() in table.pointer_type_idxs
 	if expected_type == 0 {
@@ -1104,7 +1105,8 @@ fn (mut g Gen) ref_or_deref_arg(arg ast.CallArg, expected_type table.Type) {
 				expected_type
 			}
 			deref_sym := g.table.get_type_symbol(expected_deref_type)
-			if !((arg_typ_sym.kind == .function) || deref_sym.kind in [.sum_type, .interface_]) {
+			if !((arg_typ_sym.kind == .function)
+				|| deref_sym.kind in [.sum_type, .interface_]) && lang != .c {
 				g.write('(voidptr)&/*qq*/')
 			}
 		}
diff --git a/vlib/v/gen/x64/gen.v b/vlib/v/gen/x64/gen.v
index 7c54e750f3..b13b837250 100644
--- a/vlib/v/gen/x64/gen.v
+++ b/vlib/v/gen/x64/gen.v
@@ -672,7 +672,7 @@ fn (mut g Gen) stmt(node ast.Stmt) {
 	}
 }
 
-fn C.strtol() int
+fn C.strtol(str charptr, endptr &&char, base int) int
 
 fn (mut g Gen) expr(node ast.Expr) {
 	// println('cgen expr()')
diff --git a/vlib/v/table/types.v b/vlib/v/table/types.v
index 9a846e8192..9384697a54 100644
--- a/vlib/v/table/types.v
+++ b/vlib/v/table/types.v
@@ -302,7 +302,7 @@ pub const (
 	array_type_idx         = 21
 	map_type_idx           = 22
 	chan_type_idx          = 23
-	sizet_type_idx         = 24
+	size_t_type_idx        = 24
 	any_type_idx           = 25
 	float_literal_type_idx = 26
 	int_literal_type_idx   = 27