C/C++中如何判断某一文件或目录是否存在

1.C++很简单的一种办法：


代码如下:

#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);
以前一直没用过这个函数,今天调试程序发现了这个函数,感觉挺好用,尤其是判断一个文件或文件夹是否存在的时候,用不着再find了,文件的话还可以检测读写权限,文件夹的话则只能判断是否存在,下面摘自MSDN：
int _access( const char *path, int mode );
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
Example


代码如下:

/* 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 " );
      /* Check for write permission */
      if( (_access( "ACCESS.C", 2 )) != -1 )
         printf( "File ACCESS.C has write permission " );
   }
}

OutputFile ACCESS.C existsFile 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:


代码如下:

#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：


代码如下:

///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


代码如下:

#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;
}