C/C++中判断某一文件或目录是否存在

1.C++很简单的一种办法：

#include  < iostream > 
#include  < fstream > 
using   namespace  std;
#define  FILENAME "stat.dat" 
int  main()
{
     fstream _file;
     _file.open(FILENAME,ios:: in );
      if ( ! _file)
     {
         cout << FILENAME << " 没有被创建 " ;
      }
       else 
      {
          cout << FILENAME << " 已经存在 " ;
      }
       return   0 ;
}

2.利用 c 语言的库的办法：
函数名: _access
功 能: 确定文件的访问权限
用 法: int access(const char *filename, int amode);

Determine file-access permission.

int _access( const char *path, int mode );

int _waccess( const wchar_t *path, int mode );



参考MSDN



Return Value

Each of these functions returns 0 if the file has the given mode. The function returns –1 if the named file does not exist or is not accessible in the given mode; in this case, errno is set as follows:

EACCES
Access denied: file’s permission setting does not allow specified access.
ENOENT
Filename or path not found.
Parameters
path
File or directory path
mode
Permission setting
Remarks
When used with files, the _access function determines whether the specified file exists and can be accessed as specified by the value of mode . When used with directories, _access determines only whether the specified directory exists; in Windows NT, all directories have read and write access.

mode Value Checks File For
00 Existence only
02 Write permission
04 Read permission
06 Read and write permission



Generic-Text Routine Mappings

TCHAR.H Routine	_UNICODE & _MBCS Not Defined	_MBCS Defined	_UNICODE Defined
_taccess	_access	_access	_waccess

Example

/* ACCESS.C: This example uses _access to check the
 * file named "ACCESS.C" to see if it exists and if
 * writing is allowed.
 */

#include  <io.h>
#include  <stdio.h>
#include  <stdlib.h>

void main( void )
{
   /* Check for existence */
   if( (_access( "ACCESS.C", 0 )) != -1 )
   {
      printf( "File ACCESS.C exists/n" );
      /* Check for write permission */
      if( (_access( "ACCESS.C", 2 )) != -1 )
         printf( "File ACCESS.C has write permission/n" );
   }
}

Output

File ACCESS.C exists
File ACCESS.C has write permission

3.在windows平台下用API函数FindFirstFile(...):

(1)检查文件是否存在:

#define  _WIN32_WINNT 0x0400 

#include  <windows.h> 

int main( int  argc,  char   * argv[])
{
  WIN32_FIND_DATA FindFileData;
  HANDLE hFind;

  printf ( " Target file is %s. " , argv[ 1 ]);

  hFind  =  FindFirstFile(argv[ 1 ],  & FindFileData);

   if  (hFind  ==  INVALID_HANDLE_VALUE) {
    printf ( " Invalid File Handle. Get Last Error reports %d " , GetLastError ());
  }  else  {
    printf ( " The first file found is %s " , FindFileData.cFileName);
    FindClose(hFind);
  }

   return  ( 0 );
}

(2)检查某一目录是否存在：

/// 目录是否存在的检查： 
bool   CheckFolderExist( const   string   & strPath)
{
    WIN32_FIND_DATA  wfd;
     bool  rValue  =   false ;
    HANDLE hFind  =  FindFirstFile(strPath.c_str(),  & wfd);
     if  ((hFind  !=  INVALID_HANDLE_VALUE)  &&  (wfd.dwFileAttributes  &  FILE_ATTRIBUTE_DIRECTORY))
    {
        rValue  =   true ;   
    }
    FindClose(hFind);
     return  rValue;
}

4.使用boost的filesystem类库的exists函数

#include  < boost / filesystem / operations.hpp > 
#include  < boost / filesystem / path.hpp > 
#include  < boost / filesystem / convenience.hpp > 

int  GetFilePath(std:: string   & strFilePath)
{
     string  strPath;
     int  nRes  =   0 ;

     // 指定路径             
    strPath  =   " D:/myTest/Test1/Test2 " ;
     namespace  fs  =  boost::filesystem;

     // 路径的可移植 
    fs::path full_path( fs::initial_path() );
    full_path  =  fs::system_complete( fs::path(strPath, fs::native ) );
     // 判断各级子目录是否存在，不存在则需要创建 
     if  (  ! fs::exists( full_path ) )
    {
         //  创建多层子目录 
         bool  bRet  =  fs::create_directories(full_path);
         if  ( false   ==  bRet)
        {
             return   - 1 ;
        }

    }
    strFilePath  =  full_path.native_directory_string();

     return   0 ;
}