printf.h(3head) - Linux manual page (original) (raw)
printf.h(3head) printf.h(3head)
NAME top
printf.h, register_printf_specifier, register_printf_modifier,
register_printf_type, printf_function,
printf_arginfo_size_function, printf_va_arg_function, printf_info,
PA_INT, PA_CHAR, PA_WCHAR, PA_STRING, PA_WSTRING, PA_POINTER,
PA_FLOAT, PA_DOUBLE, PA_LAST, PA_FLAG_LONG_LONG,
PA_FLAG_LONG_DOUBLE, PA_FLAG_LONG, PA_FLAG_SHORT, PA_FLAG_PTR -
define custom behavior for printf-like functionsLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <printf.h>**
**int register_printf_specifier(int** _spec_**, printf_function** _func_**,**
**printf_arginfo_size_function** _arginfo_**);**
**int register_printf_modifier(const wchar_t ***_str_**);**
**int register_printf_type(printf_va_arg_function** _fct_**);**Callbacks *typedef int printf_function(FILE *stream**, const struct printf_info ***info**, const void const args*[]);* *typedef int printf_arginfo_size_function(const struct printf_info info,* size_t n, int* argtypes[n], int size[n]); **typedef void printf_va_arg_function(void *mem**, va_list ***ap**);
Types struct printf_info { int prec; // Precision int width; // Width wchar_t spec; // Format letter unsigned int is_long_double:1;// L or ll flag unsigned int is_short:1; // h flag unsigned int is_long:1; // l flag unsigned int alt:1; // # flag unsigned int space:1; // Space flag unsigned int left:1; // - flag unsigned int showsign:1; // + flag unsigned int group:1; // ' flag unsigned int extra:1; // For special use unsigned int is_char:1; // hh flag unsigned int wide:1; // True for wide character streams unsigned int i18n:1; // I flag unsigned int is_binary128:1; /* Floating-point argument is ABI-compatible with IEC 60559 binary128 */ unsigned short user; // Bits for user-installed modifiers wchar_t pad; // Padding character };
Constants #define PA_FLAG_LONG_LONG /* ... / #define PA_FLAG_LONG_DOUBLE / ... / #define PA_FLAG_LONG / ... / #define PA_FLAG_SHORT / ... / #define PA_FLAG_PTR / ... */
DESCRIPTION top
These functions serve to extend and/or modify the behavior of the
[printf(3)](../man3/printf.3.html) family of functions.register_printf_specifier() This function registers a custom conversion specifier for the printf(3) family of functions.
_spec_ The character which will be used as a conversion specifier
in the format string.
_func_ Callback function that will be executed by the [printf(3)](../man3/printf.3.html)
family of functions to format the input arguments into the
output _stream_.
_stream_ Output stream where the formatted output should be
printed. This stream transparently represents the
output, even in the case of functions that write to
a string.
_info_ Structure that holds context information, including
the modifiers specified in the format string. This
holds the same contents as in _arginfo_.
_args_ Array of pointers to the arguments to the
[printf(3)](../man3/printf.3.html)-like function.
_arginfo_
Callback function that will be executed by the [printf(3)](../man3/printf.3.html)
family of functions to know how many arguments should be
parsed for the custom specifier and also their types.
_info_ Structure that holds context information, including
the modifiers specified in the format string. This
holds the same contents as in _func_.
_n_ Number of arguments remaining to be parsed.
_argtypes_
This array should be set to define the type of each
of the arguments that will be parsed. Each element
in the array represents one of the arguments to be
parsed, in the same order that they are passed to
the [printf(3)](../man3/printf.3.html)-like function. Each element should be
set to a base type (**PA_***) from the enum above, or a
custom one, and optionally ORed with an appropriate
length modifier (**PA_FLAG_***).
The type is determined by using one of the following
constants:
**PA_INT** _int_.
**PA_CHAR**
_int_, cast to _char_.
**PA_WCHAR**
_wchart_.
**PA_STRING**
_const char *_, a '\0'-terminated string.
**PA_WSTRING**
_const wchart *_, a wide character
L'\0'-terminated string.
**PA_POINTER**
_void *_.
**PA_FLOAT**
_float_.
**PA_DOUBLE**
_double_.
**PA_LAST**
TODO.
_size_ For user-defined types, the size of the type (in
bytes) should also be specified through this array.
Otherwise, leave it unused.
_arginfo_ is called before _func_, and prepares some information
needed to call _func_.register_printf_modifier() TODO
register_printf_type() TODO
RETURN VALUE top
**register_printf_specifier**(), **register_printf_modifier**(), and
**register_printf_type**() return zero on success, or -1 on error.Callbacks The callback of type printffunction should return the number of characters written, or -1 on error.
The callback of type _printfarginfosizefunction_ should return
the number of arguments to be parsed by this specifier. It also
passes information about the type of those arguments to the caller
through _argtypes_. On error, it should return -1.ERRORS top
**EINVAL** The specifier was not a valid character.STANDARDS top
GNU.HISTORY top
**register_printf_function**(3) is an older function similar to
**register_printf_specifier**(), and is now deprecated. That function
can't handle user-defined types.
**register_printf_specifier**() supersedes
**register_printf_function**(3).EXAMPLES top
The following example program registers the 'b' and 'B' specifiers
to print integers in binary format, mirroring rules for other
unsigned conversion specifiers like 'x' and 'u'. This can be used
to print in binary prior to C23.
/* This code is in the public domain */
#include <err.h>
#include <limits.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/param.h>
#include <printf.h>
#define GROUP_SEP '\''
struct Printf_Pad {
char ch;
size_t len;
};
static int b_printf(FILE *stream, const struct printf_info *info,
const void *const args[]);
static int b_arginf_sz(const struct printf_info *info,
size_t n, int argtypes[n], int size[n]);
static uintmax_t b_value(const struct printf_info *info,
const void *arg);
static size_t b_bin_repr(char bin[UINTMAX_WIDTH],
const struct printf_info *info, const void *arg);
static size_t b_bin_len(const struct printf_info *info,
ptrdiff_t min_len);
static size_t b_pad_len(const struct printf_info *info,
ptrdiff_t bin_len);
static ssize_t b_print_prefix(FILE *stream,
const struct printf_info *info);
static ssize_t b_pad_zeros(FILE *stream, const struct printf_info *info,
ptrdiff_t min_len);
static ssize_t b_print_number(FILE *stream,
const struct printf_info *info,
const char bin[UINTMAX_WIDTH],
size_t min_len, size_t bin_len);
static char pad_ch(const struct printf_info *info);
static ssize_t pad_spaces(FILE *stream, size_t pad_len);
int
main(void)
{
if (register_printf_specifier('b', b_printf, b_arginf_sz) == -1)
err(EXIT_FAILURE, "register_printf_specifier('b', ...)");
if (register_printf_specifier('B', b_printf, b_arginf_sz) == -1)
err(EXIT_FAILURE, "register_printf_specifier('B', ...)");
printf("....----....----....----....----\n");
printf("%llb;\n", 0x5Ellu);
printf("%lB;\n", 0x5Elu);
printf("%b;\n", 0x5Eu);
printf("%hB;\n", 0x5Eu);
printf("%hhb;\n", 0x5Eu);
printf("%jb;\n", (uintmax_t)0x5E);
printf("%zb;\n", (size_t)0x5E);
printf("....----....----....----....----\n");
printf("%#b;\n", 0x5Eu);
printf("%#B;\n", 0x5Eu);
printf("....----....----....----....----\n");
printf("%10b;\n", 0x5Eu);
printf("%010b;\n", 0x5Eu);
printf("%.10b;\n", 0x5Eu);
printf("....----....----....----....----\n");
printf("%-10B;\n", 0x5Eu);
printf("....----....----....----....----\n");
printf("%'B;\n", 0x5Eu);
printf("....----....----....----....----\n");
printf("....----....----....----....----\n");
printf("%#16.12b;\n", 0xAB);
printf("%-#'20.12b;\n", 0xAB);
printf("%#'020B;\n", 0xAB);
printf("....----....----....----....----\n");
printf("%#020B;\n", 0xAB);
printf("%'020B;\n", 0xAB);
printf("%020B;\n", 0xAB);
printf("....----....----....----....----\n");
printf("%#021B;\n", 0xAB);
printf("%'021B;\n", 0xAB);
printf("%021B;\n", 0xAB);
printf("....----....----....----....----\n");
printf("%#022B;\n", 0xAB);
printf("%'022B;\n", 0xAB);
printf("%022B;\n", 0xAB);
printf("....----....----....----....----\n");
printf("%#023B;\n", 0xAB);
printf("%'023B;\n", 0xAB);
printf("%023B;\n", 0xAB);
printf("....----....----....----....----\n");
printf("%-#'19.11b;\n", 0xAB);
printf("%#'019B;\n", 0xAB);
printf("%#019B;\n", 0xAB);
printf("....----....----....----....----\n");
printf("%'019B;\n", 0xAB);
printf("%019B;\n", 0xAB);
printf("%#016b;\n", 0xAB);
printf("....----....----....----....----\n");
return 0;
}
static int
b_printf(FILE *stream, const struct printf_info *info,
const void *const args[])
{
char bin[UINTMAX_WIDTH];
size_t min_len, bin_len;
ssize_t len, tmp;
struct Printf_Pad pad = {0};
len = 0;
min_len = b_bin_repr(bin, info, args[0]);
bin_len = b_bin_len(info, min_len);
pad.ch = pad_ch(info);
if (pad.ch == ' ')
pad.len = b_pad_len(info, bin_len);
/* Padding with ' ' (right aligned) */
if ((pad.ch == ' ') && !info->left) {
tmp = pad_spaces(stream, pad.len);
if (tmp == EOF)
return EOF;
len += tmp;
}
/* "0b"/"0B" prefix */
if (info->alt) {
tmp = b_print_prefix(stream, info);
if (tmp == EOF)
return EOF;
len += tmp;
}
/* Padding with '0' */
if (pad.ch == '0') {
tmp = b_pad_zeros(stream, info, min_len);
if (tmp == EOF)
return EOF;
len += tmp;
}
/* Print number (including leading 0s to fill precision) */
tmp = b_print_number(stream, info, bin, min_len, bin_len);
if (tmp == EOF)
return EOF;
len += tmp;
/* Padding with ' ' (left aligned) */
if (info->left) {
tmp = pad_spaces(stream, pad.len);
if (tmp == EOF)
return EOF;
len += tmp;
}
return len;
}
static int
b_arginf_sz(const struct printf_info *info, size_t n, int argtypes[n],
[[maybe_unused]] int size[n])
{
if (n < 1)
return -1;
if (info->is_long_double)
argtypes[0] = PA_INT | PA_FLAG_LONG_LONG;
else if (info->is_long)
argtypes[0] = PA_INT | PA_FLAG_LONG;
else
argtypes[0] = PA_INT;
return 1;
}
static uintmax_t
b_value(const struct printf_info *info, const void *arg)
{
if (info->is_long_double)
return *(const unsigned long long *)arg;
if (info->is_long)
return *(const unsigned long *)arg;
/* short and char are both promoted to int */
return *(const unsigned int *)arg;
}
static size_t
b_bin_repr(char bin[UINTMAX_WIDTH],
const struct printf_info *info, const void *arg)
{
size_t min_len;
uintmax_t val;
val = b_value(info, arg);
bin[0] = '0';
for (min_len = 0; val; min_len++) {
bin[min_len] = '0' + (val % 2);
val >>= 1;
}
return MAX(min_len, 1);
}
static size_t
b_bin_len(const struct printf_info *info, ptrdiff_t min_len)
{
return MAX(info->prec, min_len);
}
static size_t
b_pad_len(const struct printf_info *info, ptrdiff_t bin_len)
{
ptrdiff_t pad_len;
pad_len = info->width - bin_len;
if (info->alt)
pad_len -= 2;
if (info->group)
pad_len -= (bin_len - 1) / 4;
return MAX(pad_len, 0);
}
static ssize_t
b_print_prefix(FILE *stream, const struct printf_info *info)
{
ssize_t len;
len = 0;
if (fputc('0', stream) == EOF)
return EOF;
len++;
if (fputc(info->spec, stream) == EOF)
return EOF;
len++;
return len;
}
static ssize_t
b_pad_zeros(FILE *stream, const struct printf_info *info,
ptrdiff_t min_len)
{
ssize_t len;
ptrdiff_t tmp;
len = 0;
tmp = info->width - (info->alt * 2);
if (info->group)
tmp -= tmp / 5 - !(tmp % 5);
for (ptrdiff_t i = tmp - 1; i > min_len - 1; i--) {
if (fputc('0', stream) == EOF)
return EOF;
len++;
if (!info->group || (i % 4))
continue;
if (fputc(GROUP_SEP, stream) == EOF)
return EOF;
len++;
}
return len;
}
static ssize_t
b_print_number(FILE *stream, const struct printf_info *info,
const char bin[UINTMAX_WIDTH],
size_t min_len, size_t bin_len)
{
ssize_t len;
len = 0;
/* Print leading zeros to fill precision */
for (size_t i = bin_len - 1; i > min_len - 1; i--) {
if (fputc('0', stream) == EOF)
return EOF;
len++;
if (!info->group || (i % 4))
continue;
if (fputc(GROUP_SEP, stream) == EOF)
return EOF;
len++;
}
/* Print number */
for (size_t i = min_len - 1; i < min_len; i--) {
if (fputc(bin[i], stream) == EOF)
return EOF;
len++;
if (!info->group || (i % 4) || !i)
continue;
if (fputc(GROUP_SEP, stream) == EOF)
return EOF;
len++;
}
return len;
}
static char
pad_ch(const struct printf_info *info)
{
if ((info->prec != -1) || (info->pad == ' ') || info->left)
return ' ';
return '0';
}
static ssize_t
pad_spaces(FILE *stream, size_t pad_len)
{
ssize_t len;
len = 0;
for (size_t i = pad_len - 1; i < pad_len; i--) {
if (fputc(' ', stream) == EOF)
return EOF;
len++;
}
return len;
}SEE ALSO top
[asprintf(3)](../man3/asprintf.3.html), [printf(3)](../man3/printf.3.html), [wprintf(3)](../man3/wprintf.3.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 printf.h(3head)