??????今天系統(tǒng)莫明其妙的故障,以前用的好好的客戶信息匯總統(tǒng)計突然出現(xiàn)異常,查看日志顯示oracle的sql語句異常.
??????跟蹤調(diào)試后臺發(fā)現(xiàn)問題出現(xiàn)在sprintf語句上面,sql預定義 char[8000],然后用sprintf來格式化,結(jié)果當語句的數(shù)據(jù)超過8000的時候就不能正常處理了.
???? google了一下:
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(jié)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(jié)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(shù)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;
}