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c++ fopen和fopen_s用法的比较

点击次数:3793  更新日期:2014-07-31

在vs编程中,经常会有这样的警告:

warning C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead. To disable deprecation, use_CRT_SECURE_NO_WARNINGS. See online help for details.  

是因为  fopen_s比fopen多了溢出检测,更安全一些。(在以后的文章里还有get与get_s的比较,strcpy strcpy_s的比较,他们的共同点都是用来一些不可预料的行为,以后将进行详尽解释)

在定义FILE * fp 之后,fopen的用法是: fp = fopen(filename,"w")。而对于fopen_s来说,还得定义另外一个变量errno_t err,然后err = fopen_s(&fp,filename,"w")。返回值的话,对于fopen来说,打开文件成功的话返回文件指针(赋值给fp),打开失败则返回NULL值;对于fopen_s来说,打开文件成功返回0,失败返回非0。


#include <stdio.h>

FILE *stream, *stream2;

int main( void )
{
   int numclosed;
   errno_t err;

   // Open for read (will fail if file "crt_fopen_s.c" does not exist)
   if( (err  = fopen_s( &stream, "crt_fopen_s.c", "r" )) !=0 )
      printf( "The file 'crt_fopen_s.c' was not opened\n" );
   else
      printf( "The file 'crt_fopen_s.c' was opened\n" );

   // Open for write 
   if( (err = fopen_s( &stream2, "data2", "w+" )) != 0 )
      printf( "The file 'data2' was not opened\n" );
   else
      printf( "The file 'data2' was opened\n" );

   // Close stream if it is not NULL 
   if( stream)
   {
      if ( fclose( stream ) )
      {
         printf( "The file 'crt_fopen_s.c' was not closed\n" );
      }
   }

   // All other files are closed:
   numclosed = _fcloseall( );
   printf( "Number of files closed by _fcloseall: %u\n", numclosed );
}