register_printf_specifier(3)

—

Options · 20

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) 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)-like function.
arginfo	Callback function that will be executed by the printf(3) 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)-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_).
PA_INT	int.
PA_CHAR	int, cast to char.
PA_WCHAR	wchar_t.
PA_STRING	const char *, a '\0'-terminated string.
PA_WSTRING	const wchar_t *, 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.
EINVAL	The specifier was not a valid character.

NAME

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 functions

LIBRARY

Standard C library (libc, -lc)

SYNOPSIS

bash

#include <printf.h>

bash

int register_printf_specifier(int \nspec\n, printf_function \nfunc\n,\n
\n                              printf_arginfo_size_function \narginfo\n);\n
\nint register_printf_modifier(const wchar_t *\nstr\n);\n
\nint register_printf_type(printf_va_arg_function \nfct\n);

Callbacks

bash

typedef int printf_function(FILE *\nstream\n, const struct printf_info *\ninfo\n,\n
\n                              const void *const \nargs\n[]);\n
\ntypedef int printf_arginfo_size_function(const struct printf_info *\ninfo\n,\n
\n                              size_t \nn\n, int \nargtypes\n[\nn\n], int \nsize\n[\nn\n]);\n
\ntypedef void printf_va_arg_function(void *\nmem\n, va_list *\nap\n);

Types

bash

struct printf_info {\n
\n    int            prec;            \n// Precision
\n    int            width;           \n// Width
\n    wchar_t        spec;            \n// Format letter
\n    unsigned int   is_long_double:1;\n// \nL\n or \nll\n flag
\n    unsigned int   is_short:1;      \n// \nh\n flag
\n    unsigned int   is_long:1;       \n// \nl\n flag
\n    unsigned int   alt:1;           \n// \n#\n flag
\n    unsigned int   space:1;         \n// Space flag
\n    unsigned int   left:1;          \n// \n-\n flag
\n    unsigned int   showsign:1;      \n// \n+\n flag
\n    unsigned int   group:1;         \n// \n'\n flag
\n    unsigned int   extra:1;         \n// For special use
\n    unsigned int   is_char:1;       \n// \nhh\n flag
\n    unsigned int   wide:1;          \n// True for wide character streams
\n    unsigned int   i18n:1;          \n// \nI\n flag
\n    unsigned int   is_binary128:1;  \n/* Floating-point argument is
\n                                    \n   ABI-compatible with
\n                                    \n   IEC 60559 binary128 */
\n    unsigned short user;            \n// Bits for user-installed modifiers
\n    wchar_t        pad;             \n// Padding character
\n};\n

Constants

bash

#define PA_FLAG_LONG_LONG    \n/* ... */
\n#define PA_FLAG_LONG_DOUBLE  \n/* ... */
\n#define PA_FLAG_LONG         \n/* ... */
\n#define PA_FLAG_SHORT        \n/* ... */
\n#define PA_FLAG_PTR          \n/* ... */

DESCRIPTION

These functions serve to extend and/or modify the behavior of the printf(3) 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) 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)-like function.

arginfo: Callback function that will be executed by the printf(3) 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)-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: wchar_t.
PA_STRING: const char *, a '\0'-terminated string.
PA_WSTRING: const wchar_t *, 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

register_printf_specifier(), register_printf_modifier(), and register_printf_type() return zero on success, or -1 on error.

Callbacks

The callback of type printf_function should return the number of characters written, or -1 on error.

The callback of type printf_arginfo_size_function 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

EINVAL: The specifier was not a valid character.

/* 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 {
\n
    char    ch;
\n
    size_t  len;
};
static int b_printf(FILE *stream, const struct printf_info *info,
\n
                    const void *const args[]);
static int b_arginf_sz(const struct printf_info *info,
\n
                    size_t n, int argtypes[n], int size[n]);
static uintmax_t b_value(const struct printf_info *info,
\n
                    const void *arg);
static size_t b_bin_repr(char bin[UINTMAX_WIDTH],
\n
                    const struct printf_info *info, const void *arg);
static size_t b_bin_len(const struct printf_info *info,
\n
                    ptrdiff_t min_len);
static size_t b_pad_len(const struct printf_info *info,
\n
                    ptrdiff_t bin_len);
static ssize_t b_print_prefix(FILE *stream,
\n
                    const struct printf_info *info);
static ssize_t b_pad_zeros(FILE *stream, const struct printf_info *info,
\n
                    ptrdiff_t min_len);
static ssize_t b_print_number(FILE *stream,
\n
                    const struct printf_info *info,
\n
                    const char bin[UINTMAX_WIDTH],
\n
                    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)
{
\n
    if (register_printf_specifier('b', b_printf, b_arginf_sz) == -1)
\n
        err(EXIT_FAILURE, "register_printf_specifier('b', ...)");
\n
    if (register_printf_specifier('B', b_printf, b_arginf_sz) == -1)
\n
        err(EXIT_FAILURE, "register_printf_specifier('B', ...)");
\n
    printf("....----....----....----....----\n");
\n
    printf("%llb;\n", 0x5Ellu);
\n
    printf("%lB;\n", 0x5Elu);
\n
    printf("%b;\n", 0x5Eu);
\n
    printf("%hB;\n", 0x5Eu);
\n
    printf("%hhb;\n", 0x5Eu);
\n
    printf("%jb;\n", (uintmax_t)0x5E);
\n
    printf("%zb;\n", (size_t)0x5E);
\n
    printf("....----....----....----....----\n");
\n
    printf("%#b;\n", 0x5Eu);
\n
    printf("%#B;\n", 0x5Eu);
\n
    printf("....----....----....----....----\n");
\n
    printf("%10b;\n", 0x5Eu);
\n
    printf("%010b;\n", 0x5Eu);
\n
    printf("%.10b;\n", 0x5Eu);
\n
    printf("....----....----....----....----\n");
\n
    printf("%-10B;\n", 0x5Eu);
\n
    printf("....----....----....----....----\n");
\n
    printf("%'B;\n", 0x5Eu);
\n
    printf("....----....----....----....----\n");
\n
    printf("....----....----....----....----\n");
\n
    printf("%#16.12b;\n", 0xAB);
\n
    printf("%-#'20.12b;\n", 0xAB);
\n
    printf("%#'020B;\n", 0xAB);
\n
    printf("....----....----....----....----\n");
\n
    printf("%#020B;\n", 0xAB);
\n
    printf("%'020B;\n", 0xAB);
\n
    printf("%020B;\n", 0xAB);
\n
    printf("....----....----....----....----\n");
\n
    printf("%#021B;\n", 0xAB);
\n
    printf("%'021B;\n", 0xAB);
\n
    printf("%021B;\n", 0xAB);
\n
    printf("....----....----....----....----\n");
\n
    printf("%#022B;\n", 0xAB);
\n
    printf("%'022B;\n", 0xAB);
\n
    printf("%022B;\n", 0xAB);
\n
    printf("....----....----....----....----\n");
\n
    printf("%#023B;\n", 0xAB);
\n
    printf("%'023B;\n", 0xAB);
\n
    printf("%023B;\n", 0xAB);
\n
    printf("....----....----....----....----\n");
\n
    printf("%-#'19.11b;\n", 0xAB);
\n
    printf("%#'019B;\n", 0xAB);
\n
    printf("%#019B;\n", 0xAB);
\n
    printf("....----....----....----....----\n");
\n
    printf("%'019B;\n", 0xAB);
\n
    printf("%019B;\n", 0xAB);
\n
    printf("%#016b;\n", 0xAB);
\n
    printf("....----....----....----....----\n");
\n
    return 0;
}
static int
b_printf(FILE *stream, const struct printf_info *info,
\n
         const void *const args[])
{
\n
    char               bin[UINTMAX_WIDTH];
\n
    size_t             min_len, bin_len;
\n
    ssize_t            len, tmp;
\n
    struct Printf_Pad  pad = {0};
\n
    len = 0;
\n
    min_len = b_bin_repr(bin, info, args[0]);
\n
    bin_len = b_bin_len(info, min_len);
\n
    pad.ch = pad_ch(info);
\n
    if (pad.ch == ' ')
\n
        pad.len = b_pad_len(info, bin_len);
\n
    /* Padding with ' ' (right aligned) */
\n
    if ((pad.ch == ' ') && !info->left) {
\n
        tmp = pad_spaces(stream, pad.len);
\n
        if (tmp == EOF)
\n
            return EOF;
\n
        len += tmp;
\n
    }
\n
    /* "0b"/"0B" prefix */
\n
    if (info->alt) {
\n
        tmp = b_print_prefix(stream, info);
\n
        if (tmp == EOF)
\n
            return EOF;
\n
        len += tmp;
\n
    }
\n
    /* Padding with '0' */
\n
    if (pad.ch == '0') {
\n
        tmp = b_pad_zeros(stream, info, min_len);
\n
        if (tmp == EOF)
\n
            return EOF;
\n
        len += tmp;
\n
    }
\n
    /* Print number (including leading 0s to fill precision) */
\n
    tmp = b_print_number(stream, info, bin, min_len, bin_len);
\n
    if (tmp == EOF)
\n
        return EOF;
\n
    len += tmp;
\n
    /* Padding with ' ' (left aligned) */
\n
    if (info->left) {
\n
        tmp = pad_spaces(stream, pad.len);
\n
        if (tmp == EOF)
\n
            return EOF;
\n
        len += tmp;
\n
    }
\n
    return len;
}
static int
b_arginf_sz(const struct printf_info *info, size_t n, int argtypes[n],
\n
            [[maybe_unused]] int size[n])
{
\n
    if (n < 1)
\n
        return -1;
\n
    if (info->is_long_double)
\n
        argtypes[0] = PA_INT | PA_FLAG_LONG_LONG;
\n
    else if (info->is_long)
\n
        argtypes[0] = PA_INT | PA_FLAG_LONG;
\n
    else
\n
        argtypes[0] = PA_INT;
\n
    return 1;
}
static uintmax_t
b_value(const struct printf_info *info, const void *arg)
{
\n
    if (info->is_long_double)
\n
        return *(const unsigned long long *)arg;
\n
    if (info->is_long)
\n
        return *(const unsigned long *)arg;
\n
    /* short and char are both promoted to int */
\n
    return *(const unsigned int *)arg;
}
static size_t
b_bin_repr(char bin[UINTMAX_WIDTH],
\n
           const struct printf_info *info, const void *arg)
{
\n
    size_t     min_len;
\n
    uintmax_t  val;
\n
    val = b_value(info, arg);
\n
    bin[0] = '0';
\n
    for (min_len = 0; val; min_len++) {
\n
        bin[min_len] = '0' + (val % 2);
\n
        val >>= 1;
\n
    }
\n
    return MAX(min_len, 1);
}
static size_t
b_bin_len(const struct printf_info *info, ptrdiff_t min_len)
{
\n
    return MAX(info->prec, min_len);
}
static size_t
b_pad_len(const struct printf_info *info, ptrdiff_t bin_len)
{
\n
    ptrdiff_t  pad_len;
\n
    pad_len = info->width - bin_len;
\n
    if (info->alt)
\n
        pad_len -= 2;
\n
    if (info->group)
\n
        pad_len -= (bin_len - 1) / 4;
\n
    return MAX(pad_len, 0);
}
static ssize_t
b_print_prefix(FILE *stream, const struct printf_info *info)
{
\n
    ssize_t len;
\n
    len = 0;
\n
    if (fputc('0', stream) == EOF)
\n
        return EOF;
\n
    len++;
\n
    if (fputc(info->spec, stream) == EOF)
\n
        return EOF;
\n
    len++;
\n
    return len;
}
static ssize_t
b_pad_zeros(FILE *stream, const struct printf_info *info,
\n
            ptrdiff_t min_len)
{
\n
    ssize_t    len;
\n
    ptrdiff_t  tmp;
\n
    len = 0;
\n
    tmp = info->width - (info->alt * 2);
\n
    if (info->group)
\n
        tmp -= tmp / 5 - !(tmp % 5);
\n
    for (ptrdiff_t i = tmp - 1; i > min_len - 1; i--) {
\n
        if (fputc('0', stream) == EOF)
\n
            return EOF;
\n
        len++;
\n
        if (!info->group || (i % 4))
\n
            continue;
\n
        if (fputc(GROUP_SEP, stream) == EOF)
\n
            return EOF;
\n
        len++;
\n
    }
\n
    return len;
}
static ssize_t
b_print_number(FILE *stream, const struct printf_info *info,
\n
               const char bin[UINTMAX_WIDTH],
\n
               size_t min_len, size_t bin_len)
{
\n
    ssize_t  len;
\n
    len = 0;
\n
    /* Print leading zeros to fill precision */
\n
    for (size_t i = bin_len - 1; i > min_len - 1; i--) {
\n
        if (fputc('0', stream) == EOF)
\n
            return EOF;
\n
        len++;
\n
        if (!info->group || (i % 4))
\n
            continue;
\n
        if (fputc(GROUP_SEP, stream) == EOF)
\n
            return EOF;
\n
        len++;
\n
    }
\n
    /* Print number */
\n
    for (size_t i = min_len - 1; i < min_len; i--) {
\n
        if (fputc(bin[i], stream) == EOF)
\n
            return EOF;
\n
        len++;
\n
        if (!info->group || (i % 4) || !i)
\n
            continue;
\n
        if (fputc(GROUP_SEP, stream) == EOF)
\n
            return EOF;
\n
        len++;
\n
    }
\n
    return len;
}
static char
pad_ch(const struct printf_info *info)
{
\n
    if ((info->prec != -1) || (info->pad == ' ') || info->left)
\n
        return ' ';
\n
    return '0';
}
static ssize_t
pad_spaces(FILE *stream, size_t pad_len)
{
\n
    ssize_t  len;
\n
    len = 0;
\n
    for (size_t i = pad_len - 1; i < pad_len; i--) {
\n
        if (fputc(' ', stream) == EOF)
\n
            return EOF;
\n
        len++;
\n
    }
\n
    return len;
}

register_printf_specifier(3)

NAME

LIBRARY

SYNOPSIS

Callbacks

Types

Constants

DESCRIPTION

register_printf_specifier()

register_printf_modifier()

register_printf_type()

RETURN VALUE

Callbacks

ERRORS

STANDARDS

HISTORY

EXAMPLES

SEE ALSO