fopen和fopen_s用法的比较

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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。

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。

 

#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 ); }