精简版sprintf

#include <stdarg.h> static void t_printchar(char **str, int c) { extern int putchar(int c); if (str) { **str = c; ++(*str); } else (void)putchar(c); } #define PAD_RIGHT 1 #define PAD_ZERO 2 static int t_prints(char **out, const char *string, int width, int pad) { register int pc = 0, padchar = ' '; if (width > 0) { register int len = 0; register const char *ptr; for (ptr = string; *ptr; ++ptr) ++len; if (len >= width) width = 0; else width -= len; if (pad & PAD_ZERO) padchar = '0'; } if (!(pad & PAD_RIGHT)) { for ( ; width > 0; --width) { t_printchar (out, padchar); ++pc; } } for ( ; *string ; ++string) { t_printchar (out, *string); ++pc; } for ( ; width > 0; --width) { t_printchar (out, padchar); ++pc; } return pc; } /* the following should be enough for 32 bit int */ #define PRINT_BUF_LEN 12 static int t_printi(char **out, int i, int b, int sg, int width, int pad, int letbase) { char print_buf[PRINT_BUF_LEN]; register char *s; register int t, neg = 0, pc = 0; register unsigned int u = i; if (i == 0) { print_buf[0] = '0'; print_buf[1] = '\0'; return t_prints (out, print_buf, width, pad); } if (sg && b == 10 && i < 0) { neg = 1; u = -i; } s = print_buf + PRINT_BUF_LEN-1; *s = '\0'; while (u) { t = u % b; if( t >= 10 ) t += letbase - '0' - 10; *--s = t + '0'; u /= b; } if (neg) { if( width && (pad & PAD_ZERO) ) { t_printchar (out, '-'); ++pc; --width; } else { *--s = '-'; } } return pc + t_prints (out, s, width, pad); } static int t_print( char **out, const char *format, va_list args ) { register int width, pad; register int pc = 0; char scr[2]; for (; *format != 0; ++format) { if (*format == '%') { ++format; width = pad = 0; if (*format == '\0') break; if (*format == '%') goto out; if (*format == '-') { ++format; pad = PAD_RIGHT; } while (*format == '0') { ++format; pad |= PAD_ZERO; } for ( ; *format >= '0' && *format <= '9'; ++format) { width *= 10; width += *format - '0'; } if( *format == 's' ) { register char *s = (char *)va_arg( args, int ); pc += t_prints (out, s?s:"(null)", width, pad); continue; } if( *format == 'd' ) { pc += t_printi (out, va_arg( args, int ), 10, 1, width, pad, 'a'); continue; } if( *format == 'x' ) { pc += t_printi (out, va_arg( args, int ), 16, 0, width, pad, 'a'); continue; } if( *format == 'X' ) { pc += t_printi (out, va_arg( args, int ), 16, 0, width, pad, 'A'); continue; } if( *format == 'u' ) { pc += t_printi (out, va_arg( args, int ), 10, 0, width, pad, 'a'); continue; } if( *format == 'c' ) { /* char are converted to int then pushed on the stack */ scr[0] = (char)va_arg( args, int ); scr[1] = '\0'; pc += t_prints (out, scr, width, pad); continue; } } else { out: t_printchar (out, *format); ++pc; } } if (out) **out = '\0'; va_end( args ); return pc; } int t_printf(const char *format, ...) { va_list args; va_start( args, format ); return t_print( 0, format, args ); } int t_sprintf(char *out, const char *format, ...) { va_list args; va_start( args, format ); return t_print( &out, format, args ); } int t_snprintf( char *buf, unsigned int count, const char *format, ... ) { va_list args; ( void ) count; va_start( args, format ); return t_print( &buf, format, args ); }