Posted on 2006-09-29 10:27
小明 閱讀(34549)
評論(8) 編輯 收藏 引用 所屬分類:
C/C++
眾所周知,sprintf不能檢查目標字符串的長度，可能造成眾多安全問題,所以都會推薦使用snprintf.
snprintf(_snprintf)的聲明是這樣的
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.
最常見的錯誤用法有:
1.
char sa[256]={0};
_snprintf(sa,sizeof(sa),"%s",sb);
//錯誤原因:當sb的長度>=256的時候,sa將沒有'\0'結尾
2.
char sa[256];
_snprintf(sa,sizeof(sa)-1,"%s",sb);
//錯誤原因:當sb的長度>=255的時候,sa將沒有'\0'結尾,忘記給sa初始化
3.
char sa[256];
_snprintf(sa,sizeof(sa)-1,"%s",sb);
sa[sizeof(sa)]=0;
//錯誤原因:最后一行數組越界
正確的用法
1. //推薦用法
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;
}
2.
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;
}