在下面的示例中,我使用 C# 通过 pinvoke 调用该方法。请注意:
- 所有示例都为 "from" 提供目录路径,为 "to" 提供文件路径(这些路径实际上不存在于磁盘上)
- 我的观察结果是:
- 在 "短" MAX_PATH 长度(260)以下的路径返回预期结果。
- 一些超过 "短" MAX_PATH 的路径返回正确结果。
- 一些超过 "短" MAX_PATH 的路径返回错误答案(哎呀!)
- 一些更长的路径返回错误。但是,它没有固定的最大长度。
来源:
class Program
{
static class Native
{
// https://www.pinvoke.net/default.aspx/shlwapi.pathrelativepathto
// https://learn.microsoft.com/en-us/windows/win32/api/shlwapi/nf-shlwapi-pathrelativepathtoa
[DllImport("shlwapi.dll", SetLastError = true, CharSet = CharSet.Auto)]
[return: MarshalAs(UnmanagedType.Bool)]
internal static extern bool PathRelativePathTo([Out] StringBuilder pszPath, [In] string pszFrom, [In] int dwAttrFrom, [In] string pszTo, [In] int dwAttrTo);
}
static void Main(string[] args)
{
string pszFrom, pszTo;
int i = 0;
// #1 At "short" max path (259)
// Succeeds with right answer
pszFrom = @"c:\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCD123456789";
pszTo = @"c:\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCD123456789\abcdefghijklmnop.txt";
TestPathRelativePathTo(++i, pszFrom, pszTo);
// #2 One over "short" max path
// Succeeds with right answer
pszFrom = @"c:\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCD1234567890";
pszTo = @"c:\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCD1234567890\abcdefghijklmnop.txt";
TestPathRelativePathTo(++i, pszFrom, pszTo);
// #3 Shortest path (by experiment) that returned the wrong answer
pszFrom = @"c:\ABCDEFGHIJKLMNOPQRS\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCD1234567890";
pszTo = @"c:\ABCDEFGHIJKLMNOPQRS\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCD1234567890\b.txt";
TestPathRelativePathTo(++i, pszFrom, pszTo);
// #4: Long path that errors out
// Errors out
pszFrom = @"c:\ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGH\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
pszTo = @"c:\ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGH\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\b.txt";
TestPathRelativePathTo(++i, pszFrom, pszTo);
// #5: Same as previous except one character removed from beginning of first folder
// Succeeds, but wrong return result
pszFrom = @"c:\BCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGH\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
pszTo = @"c:\BCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGH\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\b.txt";
TestPathRelativePathTo(++i, pszFrom, pszTo);
// #6: Same as previous except 3 characters added to filename.
// Succeeds, but wrong return result
pszFrom = @"c:\BCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGH\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
pszTo = @"c:\BCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGH\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\b123.txt";
TestPathRelativePathTo(++i, pszFrom, pszTo);
}
static void TestPathRelativePathTo(int i, string pszFromDir, string pszToFile)
{
int maxResult = 10000;
StringBuilder result = new StringBuilder(maxResult);
Console.WriteLine($"#{i}: Calling PathRelativePathTo(...): pszFrom.Length: {pszFromDir.Length}; pszTo.Length {pszToFile.Length} ");
bool bRet = Native.PathRelativePathTo(result, pszFromDir, (int)FileAttributes.Directory, pszToFile, (int)FileAttributes.Normal);
if (!bRet)
{
// *Edit*: As pointed out in the comments, PathRelativePathTo does not set last error, so this part of the code is incorrect, it should really just print out that the method returned false.
// https://blogs.msdn.microsoft.com/shawnfa/2004/09/10/formatmessage-shortcut-for-win32-error-codes/
int currentError = Marshal.GetLastWin32Error();
var errorMessage = new Win32Exception(currentError).Message;
Console.WriteLine($" Error: {errorMessage}");
}
else
{
Console.WriteLine($" Result: {result}");
}
}
}
输出:
#1: Calling PathRelativePathTo(...): pszFrom.Length: 238; pszTo.Length 259
Result: .\abcdefghijklmnop.txt
#2: Calling PathRelativePathTo(...): pszFrom.Length: 239; pszTo.Length 260
Result: .\abcdefghijklmnop.txt
#3: Calling PathRelativePathTo(...): pszFrom.Length: 259; pszTo.Length 265
Result: ..\ABCD1234567890\b.txt
#4: Calling PathRelativePathTo(...): pszFrom.Length: 481; pszTo.Length 487
Error: The system cannot find the file specified
#5: Calling PathRelativePathTo(...): pszFrom.Length: 480; pszTo.Length 486
Result: .\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\b.txt
#6: Calling PathRelativePathTo(...): pszFrom.Length: 480; pszTo.Length 489
Result: .\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890\b123.txt
问题:
PathRelativePathTo
的预期行为是什么?- 它只能在“短”MAX_PATH限制下的路径上正常工作(其余行为未定义)吗?
- 是否有其他我可以使用的.NET框架而不是它(注意:我看到.NET Core有Path.GetRelativePath,但我现在不能使用它)?
PathRelativePathTo
吧,它不适用于长路径。实际上,使用它是不安全的,因为你无法指定目标缓冲区的大小,文档只说它“必须至少有 MAX_PATH 个字符大小”。 - acelent