windows中的fopen_s，fprintf_s,fscanf_s等安全增强操作函数

一 、安全增强函数   

  VS中进行编程时，经常会遇到 使用fopen不安全，建议使用fopen_s替代的警告：


    

    因为 CRT（C运行时库）中的很多函数并不进行参数的越界检测。因此windows提供了对于这些函数的安全增强版本。就是对旧版本加后缀_s ("secure") 。其中有对于文件操作的有fopen_s，fprintf_s，fscanf_s等。还有sprintf_s,strcat_s,strcpy_s等。

    这些安全增强函数并没有避免错误。只是在原来的基础上增加了安全检测。在越界时，返回错误码（设置errno值）。

 二、 fopen 与fopen_s对比

(1) 函数原型

errno_t fopen_s(
FILE** pFile,
const char *filename,
const char *mode
);

FILE *fopen(
const char* filename,
const char* mode
);

（2）返回值
fopen成功调用是返回文件指针；失败时返回NULL

fopen_s成功是返回0；失败时返回错误码

pFile	filename	mode	Return Value	Contents ofpFile
NULL	any	any	EINVAL	unchanged
any	NULL	any	EINVAL	unchanged
any	any	NULL	EINVAL	unchanged

（3）说明
使用fopen_s打开的文件时不可以共享的。
（4）示例

// This program opens two files. It uses
// fclose to close the first file and
// _fcloseall to close all remaining files.

#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 );
}执行结果：

The file 'crt_fopen_s.c' was opened The file 'data2' was opened Number of files closed by _fcloseall: 1