众所周知,sprintf不能检查目标字符串的长度，可能造成众多安全问题,所以都会推荐使用snprintf. snprintf(_snprintf)的声明是这样的 int _snprintf( char *buffer, size_t count, const char *format [, argument] ...
If len < count, then len characters are stored in buffer, a null-terminator is appended, and len is returned.
If len = count, then len characters are stored in buffer, no null-terminator is appended, and len is returned.
If len > count, then count characters are stored in buffer, no null-terminator is appended, and a negative value is returned. 最常见的错误用法有: char sa[256]={0}; _snprintf(sa,sizeof(sa),"%s",sb); //错误原因:当sb的长度>=256的时候,sa将没有'/0'结尾 char sa[256]; _snprintf(sa,sizeof(sa)-1,"%s",sb); //错误原因:当sb的长度>=255的时候,sa将没有'/0'结尾,忘记给sa初始化 char sa[256]; _snprintf(sa,sizeof(sa)-1,"%s",sb); sa[sizeof(sa)]=0; //错误原因:最后一行数组越界 正确的用法 1. //推荐用法 char sa[256]; sa[sizeof(sa)-1]=0; _snprintf(sa,sizeof(sa),"%s",sb); if(sa[sizeof(sa)-1]!=0) printf("warning:string will be truncated"); sa[sizeof(sa)-1]=0; char sa[256]={0}; int result = _snprintf(sa,sizeof(sa),"%s",sb); if(result==sizeof(sa) || result<0) printf("warning:sting will be truncated"); sa[sizeof(sa)-1]=0; }
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int snprintf(char *restrict buf, size_t n, const char * restrict format, ...);
函数说明:最多从源串中拷贝n－1个字符到目标串中，然后再在后面加一个0。所以如果目标串的大小为n
的话，将不会溢出。
函数返回值:若成功则返回欲写入的字符串长度，若出错则返回负值。
Result1(推荐的用法)
#include <stdio.h> #include <stdlib.h>
int main() char str[10]={0,}; snprintf(str, sizeof(str), "0123456789012345678"); printf("str=%s/n", str); return 0; }
root] /root/lindatest $ ./test str=012345678
Result2:(不推荐使用)
#include <stdio.h> #include <stdlib.h>
int main() char str[10]={0, }; snprintf(str, 18, "0123456789012345678"); printf("str=%s/n", str); return 0; }
root] /root/lindatest $ ./test str=01234567890123456
snprintf函数返回值的测试：
#include <stdio.h> #include <stdlib.h>
int main() char str1[10] ={0, }; char str2[10] ={0, }; int ret1=0,ret2=0; ret1=snprintf(str1, sizeof(str1), "%s", "abc"); ret2=snprintf(str2, 4, "%s", "aaabbbccc"); printf("aaabbbccc length=%d/n", strlen("aaabbbccc")); printf("str1=%s,ret1=%d/n", str1, ret1); printf("str2=%s,ret2=%d/n", str2, ret2); return 0; }
[root] /root/lindatest $ ./test aaabbbccc length=9 str1=abc,ret1=3 str2=aaa,ret2=9
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这个函数的格式跟printf的是差不多一样的, 不过在gcc里面,好像那个0是没用的,左边不会补0,会补空格, 具体格式在后文, 这是我试验的代码: 1 #include <stdio.h> 3 int main(void) 5 char array[20]; 6 char *str = "1234"; 8 snprintf(array, sizeof(array), "%08.8s", str); 9 printf("%s", array); 10 getchar(); ---------------------------------------------------------- duck@duck ~/c $ gcc -o sn snprintf.c snprintf.c: In function ‘main’: snprintf.c:8: warning: '0' flag used with ‘%s’ gnu_printf format snprintf.c:8: warning: '0' flag used with ‘%s’ gnu_printf format duck@duck ~/c $ ./sn ---------------------------------------------------------- 由上面的输出看到左边补的确实是空格.