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：

复制代码 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

复制代码 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:

复制代码 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：

复制代码 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

复制代码 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;
}