fopen_s遇到的一个问题

时间:2023-12-05 11:33:14

今天使用公司代码的日志模块记录程序运行的相关信息,发现日志总是只有两条记录,即程序启动和结束,别的都没有。跟踪了很久,终于发现是日志输出模块被我修改了一个地方:把fopen改成了fopen_s,毕竟报了warning。但是这也是问题的根源!

下面的说明来自于msdn:

Files opened by fopen_s and _wfopen_s are not sharable. If you require that a file be sharable, use _fsopen, _wfsopen with the appropriate sharing mode constant (for example, _SH_DENYNO for read/write sharing).

fopen_s打开的文件不是共享读写的!但是日志模块需要反复在同一个文件中读写,而且每次都调用了fopen_s,第二次调用的时候当然会出错了,错误代码是13,也就是EACCES (Permission denied)

这里应该使用_fsopen:

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#include <stdio.h>
#include <stdlib.h>
#include <share.h>
int main( void )
{
   FILE *stream;
   // Open output file for writing. Using _fsopen allows us to
   // ensure that no one else writes to the file while we are
   // writing to it.
    //
   if( (stream = _fsopen( "outfile", "wt", _SH_DENYWR )) != NULL )
   {
      fprintf( stream, "No one else in the network can write "
                       "to this file until we are done.\n" );
      fclose( stream );
   }
   // Now others can write to the file while we read it.
   system( "type outfile" );
}

(以上代码来自于msdn,版权归原作者所有)