os: implement os.write_file_array and os.read_file_array .

vlib/os/os.v

@@ -60,18 +60,19 @@ pub fn (mut f File) writeln(s string) {
 	C.fputs('\n', f.cfile)
 }
 
-pub fn (mut f File) write_bytes(data voidptr, size int) {
+pub fn (mut f File) write_bytes(data voidptr, size int) int {
-	C.fwrite(data, 1, size, f.cfile)
+	return C.fwrite(data, 1, size, f.cfile)
 }
 
-pub fn (mut f File) write_bytes_at(data voidptr, size, pos int) {
+pub fn (mut f File) write_bytes_at(data voidptr, size, pos int) int {
 	//$if linux {
 	//}
 	//$else {
 	C.fseek(f.cfile, pos, C.SEEK_SET)
-	C.fwrite(data, 1, size, f.cfile)
+	res := C.fwrite(data, 1, size, f.cfile)
 	C.fseek(f.cfile, 0, C.SEEK_END)
 	//}
+	return res
 }
 
 /***************************** Read ops  ****************************/
@@ -887,6 +888,35 @@ pub fn write_file(path, text string) ? {
 	f.close()
 }
 
+// write_file_array writes the data in `buffer` to a file in `path`.
+pub fn write_file_array(path string, buffer array) ? {
+	mut f := os.create(path) or {
+		return error(err)
+	}
+	f.write_bytes_at(buffer.data, (buffer.len * buffer.element_size), 0)
+	f.close()
+}
+
+// read_file_array reads an array of `T` values from file `path`
+pub fn read_file_array<T>(path string) []T {
+	a := T{}
+	tsize := int(sizeof(a))    
+	// prepare for reading, get current file size
+	mut fp := vfopen(path, 'rb')
+	if isnil(fp) {
+		return array{}
+	}
+	C.fseek(fp, 0, C.SEEK_END)
+	fsize := C.ftell(fp)
+	C.rewind(fp)
+	// read the actual data from the file
+	len := fsize / tsize
+	buf := malloc(fsize)
+	C.fread(buf, fsize, 1, fp)
+	C.fclose(fp)    
+	return array{element_size: tsize data: buf len: len cap: len }
+}
+
 pub fn on_segfault(f voidptr) {
 	$if windows {
 		return

vlib/os/os_test.v

@@ -20,6 +20,7 @@ fn testsuite_end() {
 	os.chdir( os.wd_at_startup )
 	os.rmdir_all( tfolder )
 	assert !os.is_dir( tfolder )
+	//eprintln('testsuite_end  , tfolder = $tfolder removed.')
 }
 
 fn test_open_file() {
@@ -352,3 +353,41 @@ fn test_uname() {
 	assert u.version.len > 0
 	assert u.machine.len > 0
 }
+
+// tests for write_file_array and read_file_array<T>:
+const (
+	maxn = 3
+)
+
+struct IntPoint {
+	x int
+	y int
+}
+
+fn test_write_file_array_bytes() {
+	fpath := './abytes.bin'
+	mut arr := []byte{len: maxn}
+	for i in 0 .. maxn {
+		arr[i] = 65 + byte(i)
+	}
+	os.write_file_array(fpath, arr)
+	rarr := os.read_bytes(fpath) or {
+		panic(err)
+	}
+	assert arr == rarr
+	//eprintln(arr.str())
+	//eprintln(rarr.str())
+}
+
+fn test_write_file_array_structs() {
+	fpath := './astructs.bin'
+	mut arr := []IntPoint{len: maxn}
+	for i in 0 .. maxn {
+		arr[i] = IntPoint{65 + i, 65 + i + 10}
+	}
+	os.write_file_array(fpath, arr)
+	rarr := os.read_file_array<IntPoint>(fpath)
+	assert rarr == arr
+	assert rarr.len == maxn
+	//eprintln( rarr.str().replace('\n', ' ').replace('},', '},\n'))
+}