7.6 KiB
v_printf/v_sprintf
These are v implementations of the C language printf and sprintf functions.
Note: These functions are platform dependent in C, but in V they are platform independent.
v_sprintf
v_sprintf has a variable number of parameters.
The first is a format string to control the appearance of the final string.
Each format specifier (%s, %d, etc.) in the format string
is replaced by the textual version of the following parameters.
import strconv
fn main() {
a := 'World'
s := strconv.v_sprintf('Hello %s!', a)
println(s)
}
Hello World!
v_printf
v_printf creates the same modified string as v_sprintf, using the same format specifiers,
but it will immediately print the modified string to stdout instead of returning a string.
Syntax
The syntax for a format specifier is:
%[parameter][flags][width][.precision][length]type
Flags field
The Flags field may be zero or more (in any order) of:
| Character | Description |
|---|---|
- (minus) |
Left-align the output of this specifier. (The default is to right-align the output.) |
+ (plus) |
Prepends a plus for positive signed-numeric types. positive = +, negative = -. (The default doesn't prepend anything to positive numbers.) |
0 (zero) |
When the 'width' option is specified, prepends zeros for numeric types. (The default prepends spaces.) For example, printf("%4X",3) produces 3, while printf("%04X",3) produces 0003. |
Width field
The Width field specifies a maximum number of characters to output, and is typically used to pad fixed-width fields in tabulated output, it causes truncation of oversized fields.
The width field may be omitted, or it may be a numeric integer value,
or may also be specified by a parameter when indicated by an asterisk *.
For example, v_printf("%*.s", 5, my_string) will result in mystring being printed,
with a total width of 5 characters.
Length field
The Length field can be omitted or be any of:
| Character | Description |
|---|---|
hh |
For integer types, causes printf to expect an byte or i8 argument. |
h |
For integer types, causes printf to expect an int16 or u16 argument. |
l |
For integer types, causes printf to expect an i64 or u64 argument. |
ll |
For integer types, causes printf to expect an i64 or u64 argument. |
Type field
The Type field can be any of:
| Character | Description |
|---|---|
% |
Prints a literal % character (this type doesn't accept any flags, width, precision, length fields). |
d, i |
int as a signed int %d and %i are synonymous for output. The size of the argument is specified by the length field. |
u |
unsigned int. The size of the argument is specified by the length field. |
f, F |
double in normal notation. f and F only differs in how the strings are printed: lowercase or uppercase. |
e, E |
double in scientific notation.e and E only differs in how the strings are printed: lowercase or uppercase. |
g, G |
double in automatic notation.g and G only differs in how the strings are printed: lowercase or uppercase. |
x, X |
unsigned int as a hexadecimal number. x uses lower-case letters and X uses upper-case. |
s |
string |
p |
void * (pointer to void) in an implementation-defined format. |
c |
char (character). |
Examples
various types
import strconv
a0 := u32(10)
b0 := 200
c0 := byte(12)
s0 := 'ciAo'
ch0 := `B`
f0 := 0.312345
f1 := 200000.0
sc0 := 'ciao: [%-08u] %d %hhd [%8s] [%08X] [%-20.4f] [%-20.4f] [%c]'
temp_s := strconv.v_sprintf(sc0, a0, b0, c0, s0, b0, f0, f1, ch0)
println(temp_s)
ciao: [10 ] 200 12 [ ciAo] [000000C8] [0.3123 ] [200000.0000 ] [B]
integer
import strconv
a := byte(12)
b := i16(13)
c := 14
d := i64(15)
sc1 := '==>%hhd %hd %d %ld'
temp_s := strconv.v_sprintf(sc1, a, b, c, d)
println(temp_s)
==>12 13 14 15
unsigned integer
import strconv
a1 := byte(0xff)
b1 := u16(0xffff)
c1 := u32(0xffffffff)
d1 := u64(-1)
sc2 := '%hhu %hu %u %lu'
temp_s := strconv.v_sprintf(sc2, a1, b1, c1, d1)
println(temp_s)
255 65535 4294967295 18446744073709551615
hexadecimal
import strconv
a1 := byte(0xff)
b1 := i16(0xffff)
c1 := u32(0xffffffff)
d1 := u64(-1)
sc3 := '%hhx %hx %x %lx'
temp_s := strconv.v_sprintf(sc3, a1, b1, c1, d1)
println(temp_s)
ff ffff ffffffff ffffffffffffffff
hexadecimal
import strconv
a2 := 125
sc7 := '[%9x] [%9X] [%-9x] [%-9X] [%09x] [%09X]'
temp_s := strconv.v_sprintf(sc7, a2, a2, a2, a2, a2, a2)
println(temp_s)
[ 7d] [ 7D] [7d ] [7D ] [00000007d] [00000007D]
floating points
import strconv
f0 := 0.312345
f1 := 200000.0
f2 := -1234.300e6
f3 := 1234.300e-6
sc4 := '[%-20.3e] [%20.3e] [%-020.3e] [%-020.3E] [%-020.3e] [%-020.3e]'
temp_s := strconv.v_sprintf(sc4, f0, f1, f1, f1, f2, f3)
println(temp_s)
[3.123e-01 ] [ 2.000e+05] [2.000e+05 ] [2.000E+05 ] [-1.234e+09 ] [1.234e-03 ]
float automatic notations
import strconv
mut ft := -1e-7
mut x := 0
sc8 := '[%20g][%20G]|'
for x < 12 {
temp_s := strconv.v_sprintf(sc8, ft, ft)
println('$temp_s\n')
ft = ft * 10.0
x++
}
[ -1e-07][ -1E-07]|
[ -1e-06][ -1E-06]|
[ -1e-05][ -1E-05]|
[ -0.0001][ -0.0001]|
[ -0.001][ -0.001]|
[ -0.01][ -0.01]|
[ -0.1][ -0.1]|
[ -1][ -1]|
[ -10][ -10]|
[ -100][ -100]|
[ -1000][ -1000]|
[ -10000][ -10000]|
Utility functions
The format module also has some utility functions:
// calling struct
struct BF_param {
pad_ch byte = ` ` // padding char
len0 int = -1 // default len for whole the number or string
len1 int = 6 // number of decimal digits, if needed
positive bool = true // mandatory: the sign of the number passed
sign_flag bool = false // flag for print sign as prefix in padding
allign Align_text = .right // alignment of the string
rm_tail_zero bool = false // remove the tail zeros from floats
}
// utilities
fn format_dec(d u64, p BF_param) string
fn format_fl(f f64, p BF_param) string
fn format_es(f f64, p BF_param) string
fn remove_tail_zeros(s string) string
format_dec format the integer number using the parameters in the BF_param struct.
format_fl format a float number in normal notation using the parameters in the BF_param struct.
format_es format a float number in scientific notation using the parameters in the BF_param
struct.
remove_tail_zeros removes the tailing zeros from a floating point number as string.