判断文件是否存在

函数如下：

inline bool is_file_exist(const std::string& filepath)
{
    struct  _stat buffer;
    return _stat(filepath.c_str(), &buffer) == 0;
}

_stat， _wstat函数用于获取文件的状态信息。
函数返加0表进成功，为-1表示失败即文件不存在。

参考链接：https://learn.microsoft.com/zh-cn/previous-versions/14h5k7ff(v=vs.110)

// crt_stat.c
// This program uses the _stat function to
// report information about the file named crt_stat.c.

#include <time.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <errno.h>

int main( void )
{
   struct _stat buf;
   int result;
   char timebuf[26];
   char* filename = "crt_stat.c";
   errno_t err;

   // Get data associated with "crt_stat.c": 
   result = _stat( filename, &buf );

   // Check if statistics are valid: 
   if( result != 0 )
   {
      perror( "Problem getting information" );
      switch (errno)
      {
         case ENOENT:
           printf("File %s not found.\n", filename);
           break;
         case EINVAL:
           printf("Invalid parameter to _stat.\n");
           break;
         default:
           /* Should never be reached. */
           printf("Unexpected error in _stat.\n");
      }
   }
   else
   {
      // Output some of the statistics: 
      printf( "File size     : %ld\n", buf.st_size );
      printf( "Drive         : %c:\n", buf.st_dev + 'A' );
      err = ctime_s(timebuf, 26, &buf.st_mtime);
      if (err)
      {
         printf("Invalid arguments to ctime_s.");
         exit(1);
      }
      printf( "Time modified : %s", timebuf );
   }
}