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，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，如下：

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)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;
}