如何访问超长文件

现在，又回归到代码编写了。

其实，安安静静地享受编码的过程，是一个很美好的旅程，从此以后，就尽情享受这一过程吧。

现在，就遇到了在Windows上如何访问和操作超长文件（长度超过256）的问题。此前一直使用open、read、write等Windows原始开发接口，为照顾和Linux、Unix等接口类型的兼容性，没有使用Win32的SDK接口，这下搞不定了。

经过本次调研，发现访问超长文件名的方法，基本上有两种

一、将文件名缩短成8.3格式，继续使用原始开发接口来操作

The GetShortPathName function retrieves the short path form of a specified input path.

DWORD GetShortPathName(
  LPCTSTR lpszLongPath,  // null-terminated path string
  LPTSTR lpszShortPath,  // short form buffer
  DWORD cchBuffer        // size of short form buffer
);

Parameters

lpszLongPath

[in] Pointer to a null-terminated path string. The function retrieves the short form of this path.

Windows NT/2000/XP: In the ANSI version of this function, the name is limited to MAX_PATH characters. To extend this
limit to nearly 32,000 wide characters, call the Unicode version of the function and prepend "\\?\" to the path. For more information, see File
Name Conventions.

Windows 95/98/Me: This string must not exceed MAX_PATH characters.

lpszShortPath

[out] Pointer to a buffer to receive the null-terminated short form of the path specified by lpszLongPath.

cchBuffer

[in] Specifies the size, in TCHARs, of the buffer pointed to by lpszShortPath.

Return Values

If the function succeeds, the return value is the length, in TCHARs, of the string copied to lpszShortPath,
not including the terminating null character.

If the lpszShortPath buffer is too small to contain the path, the return value is the size of the buffer, in TCHARs,
required to hold the path. Therefore, if the return value is greater than cchBuffer, call the function again with a buffer that is large enough to hold the path.

If the function fails for any other reason, the return value is zero. To get extended error information, call GetLastError.

从lpszLongPath参数的说明可以看出，GetShortPathNameW函数，可以对目录或文件名进行缩短，但有个前提是目录或文件名必须存在。即

1）对于已经存在的目录或文件，适用；

2）对于不存在的目录或文件（新建目录或文件时），不适用；

二、借用Win32接口来实现对超长文件名的文件或目录的操作

其中，涉及到如下的函数

举个创建或打开文件的例子吧，

<span style="font-size:14px;">HANDLE T_FileOpen_Win32(const char *filename, int oflag, int mode)
{
	int ret = 0;
	HANDLE Handle = INVALID_HANDLE_VALUE;
	WCHAR tFileName[WTP_FULL_FILENAME_LEN+1]={0};
	char apiFileName[WTP_FULL_FILENAME_LEN+1]={0};

	strcat(apiFileName,"\\\\\?\\");
	strcat(apiFileName,filename);

	ret = MultiByteToWideChar (CP_ACP, 0, apiFileName, strlen (apiFileName) + 1, tFileName, sizeof(tFileName)/sizeof(tFileName[0])) ;
	Handle = CreateFileW(tFileName, mode,FILE_SHARE_READ,NULL,oflag,FILE_ATTRIBUTE_NORMAL,NULL);
	ret = GetLastError();

	return Handle;
}</span>

如何使用呢？

1）创建或打开文件

logFileFd = T_FileOpen_Win32(transLogFileFullName,OPEN_ALWAYS,GENERIC_WRITE|GENERIC_READ);

2）只打开文件

logFileFd = T_FileOpen_Win32(transLogFileFullName,OPEN_EXISTING,GENERIC_WRITE|GENERIC_READ);

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如何访问超长文件