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strconv: v_printf documentation

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* v_printf documentation

* syntax fix
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penguindark
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# 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.
```v
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
```v
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
```v
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
```v
a1 := byte(0xff)
b1 := u16(0xffff)
c1 := u32(0xffff_ffff)
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
```v
a1 := byte(0xff)
b1 := i16(0xffff)
c1 := u32(0xffff_ffff)
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
```v
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
```v
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
```v
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:
```v
// 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.