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); 
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
/* 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 " );   
     }
}

/*
Output
File 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:
#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;
}