# printf.h

## 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



           **#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



           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.
    


## STANDARDS



           GNU.
    


## EXAMPLES



           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;
           }
    


* * *