函数
int printf(const char *format, ... );/* [until c99]写结果到stdout */int printf(const char *restrict format, ... );/* [since c99] */int fprintf(FILE *stream, const char *format, ... );/* [until c99]写结果到文件流stream */int fprintf(FILE *restrict stream, const char *restrict format, ... );int sprintf(char *dest, const char *format, ... );/* [until c99]写结果至dest */int sprintf(char *restrict dest, const char *restrict format, ... );int snprintf(char *restrict dest, size_t bufsz, const char *restrict format, ... );/* [since c99]写结果至dest，至多写bufsz-1个字符。产生的字符串会以空字符终止，除非bufsz为0。若bufsz为0，则不写入任何内容，且dest可以是空指针，然而依旧计算返回值（会写入的字符数，不包含空终止符）并返回。 */int vprintf(const char *format, va_list ap);int vprintf(const char *restrict format, va_list ap);int vfprintf(FILE *stream, const char *format, va_list ap);int vfprintf(FILE *restrict stream, const char *restrict format, va_list ap);int vsprintf(char *dest, const char *format, va_list ap);int vsprintf(char *restrict dest, const char *restrict format, va_list ap);int vsnprintf(char *restrict dest, size_t bufsz, const char *restrict format, va_list ap);
参数
stream -- 要写入的输出文件流bufsz -- 最多写入bufsz-1个字符，再加上空终止符format -- 指向指定数据转译方式的空终止多字节字符串的指针
Example
#include <stdio.h>int main(){/* String test */char *str = "hello";printf("str = .%s.\r\n", str);printf("str = .%-10s.\r\n", str);printf("str = .%10s.\r\n", str);printf("str = .%-*s.\r\n", 10, str);printf("str = .%*s.\r\n", 10, str);printf("str = .%*.*s.\r\n", 10, 5, str);printf("str = .%*.*s.\r\n", 10, 2, str);printf("str = .%10.5s.\r\n", str);printf("str = .%10.2s.\r\n", str);/* Integer test */printf("dec = .%d.\r\n", 555);printf("dec = .%10d.\r\n", 555);printf("dec = .%10.5d.\r\n", 555);printf("dec = .%-10.5d.\r\n", 555);printf("dec = .%*.*d.\r\n", 10, 5, 555);printf("dec = .%*.*d.\r\n", 10, 2, 555);printf("hex = .%x.\r\n", 555);printf("hex = .%X.\r\n", 555);printf("hex = .%#x.\r\n", 555);printf("hex = .%10x.\r\n", 555);printf("hex = .%10.5x.\r\n", 555);printf("hex = .%-10.5x.\r\n", 555);printf("hex = .%*.*x.\r\n", 10, 5, 555);printf("hex = .%*.*x.\r\n", 10, 2, 555);printf("oct = .%o.\r\n", 555);printf("oct = .%#o.\r\n", 555);printf("oct = .%10o.\r\n", 555);printf("oct = .%10.5o.\r\n", 555);printf("oct = .%-10.5o.\r\n", 555);printf("oct = .%*.*o.\r\n", 10, 5, 555);printf("oct = .%*.*o.\r\n", 10, 2, 555);/* Float test */printf("flt = .%f.\r\n", 3.1415);printf("flt = .%lf.\r\n", 3.1415);printf("flt = .%10f.\r\n", 3.1415);printf("flt = .%10.5f.\r\n", 3.1415);printf("flt = .%-10.5f.\r\n", 3.1415);printf("flt = .%*.*f.\r\n", 10, 5, 3.1415);printf("flt = .%*.*f.\r\n", 10, 2, 3.1415);return 0;}/* 运行结果 */str = .hello.str = .hello .str = . hello.str = .hello .str = . hello.str = . hello.str = . he.str = . hello.str = . he.dec = .555.dec = . 555.dec = . 00555.dec = .00555 .dec = . 00555.dec = . 555.hex = .22b.hex = .22B.hex = .0x22b.hex = . 22b.hex = . 0022b.hex = .0022b .hex = . 0022b.hex = . 22b.oct = .1053.oct = .01053.oct = . 1053.oct = . 01053.oct = .01053 .oct = . 01053.oct = . 1053.flt = .3.141500.flt = .3.141500.flt = . 3.141500.flt = . 3.14150.flt = .3.14150 .flt = . 3.14150.flt = . 3.14./* snprintf实现strlen功能 */#include <stdio.h>#include <string.h>int main(){char *str = "helloworld";int slen = snprintf(NULL, 0, "%s", str);printf("%d - %ld\r\n",slen, strlen(str));return 0;}#include <stdio.h>#include <stdarg.h>#include <time.h>void debug_log(const char *fmt, ...){struct timespec ts;timespec_get(&ts, TIME_UTC);char time_buf[100];size_t rc = strftime(time_buf, sizeof time_buf, "%D %T", gmtime(&ts.tv_sec));snprintf(time_buf + rc, sizeof time_buf - rc, ".%06ld UTC", ts.tv_nsec / 1000);va_list args1;va_start(args1, fmt);va_list args2;va_copy(args2, args1);char buf[1+vsnprintf(NULL, 0, fmt, args1)];va_end(args1);vsnprintf(buf, sizeof buf, fmt, args2);va_end(args2);printf("%s [debug]: %s\n", time_buf, buf);}int main(void){debug_log("Logging, %d, %d, %d", 1, 2, 3);}
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