正如 above 所指出的，.NET Core 2.x 实现了 Path.GetRelativePath。
以下代码改编自源代码，适用于 .NET 4.7.1 Framework。
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
//Adapted from https://github.com/dotnet/corefx/blob/master/src/Common/src/CoreLib/System/IO/Path.cs#L697
// by Anton Krouglov
using System.Runtime.CompilerServices;
using System.Diagnostics;
using System.Text;
using Xunit;
namespace System.IO {
// Provides methods for processing file system strings in a cross-platform manner.
// Most of the methods don't do a complete parsing (such as examining a UNC hostname),
// but they will handle most string operations.
public static class PathNetCore {
/// <summary>
/// Create a relative path from one path to another. Paths will be resolved before calculating the difference.
/// Default path comparison for the active platform will be used (OrdinalIgnoreCase for Windows or Mac, Ordinal for Unix).
/// </summary>
/// <param name="relativeTo">The source path the output should be relative to. This path is always considered to be a directory.</param>
/// <param name="path">The destination path.</param>
/// <returns>The relative path or <paramref name="path"/> if the paths don't share the same root.</returns>
/// <exception cref="ArgumentNullException">Thrown if <paramref name="relativeTo"/> or <paramref name="path"/> is <c>null</c> or an empty string.</exception>
public static string GetRelativePath(string relativeTo, string path) {
return GetRelativePath(relativeTo, path, StringComparison);
}
private static string GetRelativePath(string relativeTo, string path, StringComparison comparisonType) {
if (string.IsNullOrEmpty(relativeTo)) throw new ArgumentNullException(nameof(relativeTo));
if (string.IsNullOrEmpty(path)) throw new ArgumentNullException(nameof(path));
Debug.Assert(comparisonType == StringComparison.Ordinal ||
comparisonType == StringComparison.OrdinalIgnoreCase);
relativeTo = Path.GetFullPath(relativeTo);
path = Path.GetFullPath(path);
// Need to check if the roots are different- if they are we need to return the "to" path.
if (!PathInternalNetCore.AreRootsEqual(relativeTo, path, comparisonType))
return path;
int commonLength = PathInternalNetCore.GetCommonPathLength(relativeTo, path,
ignoreCase: comparisonType == StringComparison.OrdinalIgnoreCase);
// If there is nothing in common they can't share the same root, return the "to" path as is.
if (commonLength == 0)
return path;
// Trailing separators aren't significant for comparison
int relativeToLength = relativeTo.Length;
if (PathInternalNetCore.EndsInDirectorySeparator(relativeTo))
relativeToLength--;
bool pathEndsInSeparator = PathInternalNetCore.EndsInDirectorySeparator(path);
int pathLength = path.Length;
if (pathEndsInSeparator)
pathLength--;
// If we have effectively the same path, return "."
if (relativeToLength == pathLength && commonLength >= relativeToLength) return ".";
// We have the same root, we need to calculate the difference now using the
// common Length and Segment count past the length.
//
// Some examples:
//
// C:\Foo C:\Bar L3, S1 -> ..\Bar
// C:\Foo C:\Foo\Bar L6, S0 -> Bar
// C:\Foo\Bar C:\Bar\Bar L3, S2 -> ..\..\Bar\Bar
// C:\Foo\Foo C:\Foo\Bar L7, S1 -> ..\Bar
StringBuilder
sb = new StringBuilder(); //StringBuilderCache.Acquire(Math.Max(relativeTo.Length, path.Length));
// Add parent segments for segments past the common on the "from" path
if (commonLength < relativeToLength) {
sb.Append("..");
for (int i = commonLength + 1; i < relativeToLength; i++) {
if (PathInternalNetCore.IsDirectorySeparator(relativeTo[i])) {
sb.Append(DirectorySeparatorChar);
sb.Append("..");
}
}
}
else if (PathInternalNetCore.IsDirectorySeparator(path[commonLength])) {
// No parent segments and we need to eat the initial separator
// (C:\Foo C:\Foo\Bar case)
commonLength++;
}
// Now add the rest of the "to" path, adding back the trailing separator
int differenceLength = pathLength - commonLength;
if (pathEndsInSeparator)
differenceLength++;
if (differenceLength > 0) {
if (sb.Length > 0) {
sb.Append(DirectorySeparatorChar);
}
sb.Append(path, commonLength, differenceLength);
}
return sb.ToString(); //StringBuilderCache.GetStringAndRelease(sb);
}
// Public static readonly variant of the separators. The Path implementation itself is using
// internal const variant of the separators for better performance.
public static readonly char DirectorySeparatorChar = PathInternalNetCore.DirectorySeparatorChar;
public static readonly char AltDirectorySeparatorChar = PathInternalNetCore.AltDirectorySeparatorChar;
public static readonly char VolumeSeparatorChar = PathInternalNetCore.VolumeSeparatorChar;
public static readonly char PathSeparator = PathInternalNetCore.PathSeparator;
/// <summary>Returns a comparison that can be used to compare file and directory names for equality.</summary>
internal static StringComparison StringComparison => StringComparison.OrdinalIgnoreCase;
}
/// <summary>Contains internal path helpers that are shared between many projects.</summary>
internal static class PathInternalNetCore {
internal const char DirectorySeparatorChar = '\\';
internal const char AltDirectorySeparatorChar = '/';
internal const char VolumeSeparatorChar = ':';
internal const char PathSeparator = ';';
internal const string ExtendedDevicePathPrefix = @"\\?\";
internal const string UncPathPrefix = @"\\";
internal const string UncDevicePrefixToInsert = @"?\UNC\";
internal const string UncExtendedPathPrefix = @"\\?\UNC\";
internal const string DevicePathPrefix = @"\\.\";
//internal const int MaxShortPath = 260;
// \\?\, \\.\, \??\
internal const int DevicePrefixLength = 4;
/// <summary>
/// Returns true if the two paths have the same root
/// </summary>
internal static bool AreRootsEqual(string first, string second, StringComparison comparisonType) {
int firstRootLength = GetRootLength(first);
int secondRootLength = GetRootLength(second);
return firstRootLength == secondRootLength
&& string.Compare(
strA: first,
indexA: 0,
strB: second,
indexB: 0,
length: firstRootLength,
comparisonType: comparisonType) == 0;
}
/// <summary>
/// Gets the length of the root of the path (drive, share, etc.).
/// </summary>
internal static int GetRootLength(string path) {
int i = 0;
int volumeSeparatorLength = 2; // Length to the colon "C:"
int uncRootLength = 2; // Length to the start of the server name "\\"
bool extendedSyntax = path.StartsWith(ExtendedDevicePathPrefix);
bool extendedUncSyntax = path.StartsWith(UncExtendedPathPrefix);
if (extendedSyntax) {
// Shift the position we look for the root from to account for the extended prefix
if (extendedUncSyntax) {
// "\\" -> "\\?\UNC\"
uncRootLength = UncExtendedPathPrefix.Length;
}
else {
// "C:" -> "\\?\C:"
volumeSeparatorLength += ExtendedDevicePathPrefix.Length;
}
}
if ((!extendedSyntax || extendedUncSyntax) && path.Length > 0 && IsDirectorySeparator(path[0])) {
// UNC or simple rooted path (e.g. "\foo", NOT "\\?\C:\foo")
i = 1; // Drive rooted (\foo) is one character
if (extendedUncSyntax || (path.Length > 1 && IsDirectorySeparator(path[1]))) {
// UNC (\\?\UNC\ or \\), scan past the next two directory separators at most
// (e.g. to \\?\UNC\Server\Share or \\Server\Share\)
i = uncRootLength;
int n = 2; // Maximum separators to skip
while (i < path.Length && (!IsDirectorySeparator(path[i]) || --n > 0)) i++;
}
}
else if (path.Length >= volumeSeparatorLength &&
path[volumeSeparatorLength - 1] == PathNetCore.VolumeSeparatorChar) {
// Path is at least longer than where we expect a colon, and has a colon (\\?\A:, A:)
// If the colon is followed by a directory separator, move past it
i = volumeSeparatorLength;
if (path.Length >= volumeSeparatorLength + 1 && IsDirectorySeparator(path[volumeSeparatorLength])) i++;
}
return i;
}
/// <summary>
/// True if the given character is a directory separator.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal static bool IsDirectorySeparator(char c) {
return c == PathNetCore.DirectorySeparatorChar || c == PathNetCore.AltDirectorySeparatorChar;
}
/// <summary>
/// Get the common path length from the start of the string.
/// </summary>
internal static int GetCommonPathLength(string first, string second, bool ignoreCase) {
int commonChars = EqualStartingCharacterCount(first, second, ignoreCase: ignoreCase);
// If nothing matches
if (commonChars == 0)
return commonChars;
// Or we're a full string and equal length or match to a separator
if (commonChars == first.Length
&& (commonChars == second.Length || IsDirectorySeparator(second[commonChars])))
return commonChars;
if (commonChars == second.Length && IsDirectorySeparator(first[commonChars]))
return commonChars;
// It's possible we matched somewhere in the middle of a segment e.g. C:\Foodie and C:\Foobar.
while (commonChars > 0 && !IsDirectorySeparator(first[commonChars - 1]))
commonChars--;
return commonChars;
}
/// <summary>
/// Gets the count of common characters from the left optionally ignoring case
/// </summary>
internal static unsafe int EqualStartingCharacterCount(string first, string second, bool ignoreCase) {
if (string.IsNullOrEmpty(first) || string.IsNullOrEmpty(second)) return 0;
int commonChars = 0;
fixed (char* f = first)
fixed (char* s = second) {
char* l = f;
char* r = s;
char* leftEnd = l + first.Length;
char* rightEnd = r + second.Length;
while (l != leftEnd && r != rightEnd
&& (*l == *r || (ignoreCase &&
char.ToUpperInvariant((*l)) == char.ToUpperInvariant((*r))))) {
commonChars++;
l++;
r++;
}
}
return commonChars;
}
/// <summary>
/// Returns true if the path ends in a directory separator.
/// </summary>
internal static bool EndsInDirectorySeparator(string path)
=> path.Length > 0 && IsDirectorySeparator(path[path.Length - 1]);
}
/// <summary> Tests for PathNetCore.GetRelativePath </summary>
public static class GetRelativePathTests {
[Theory]
[InlineData(@"C:\", @"C:\", @".")]
[InlineData(@"C:\a", @"C:\a\", @".")]
[InlineData(@"C:\A", @"C:\a\", @".")]
[InlineData(@"C:\a\", @"C:\a", @".")]
[InlineData(@"C:\", @"C:\b", @"b")]
[InlineData(@"C:\a", @"C:\b", @"..\b")]
[InlineData(@"C:\a", @"C:\b\", @"..\b\")]
[InlineData(@"C:\a\b", @"C:\a", @"..")]
[InlineData(@"C:\a\b", @"C:\a\", @"..")]
[InlineData(@"C:\a\b\", @"C:\a", @"..")]
[InlineData(@"C:\a\b\", @"C:\a\", @"..")]
[InlineData(@"C:\a\b\c", @"C:\a\b", @"..")]
[InlineData(@"C:\a\b\c", @"C:\a\b\", @"..")]
[InlineData(@"C:\a\b\c", @"C:\a", @"..\..")]
[InlineData(@"C:\a\b\c", @"C:\a\", @"..\..")]
[InlineData(@"C:\a\b\c\", @"C:\a\b", @"..")]
[InlineData(@"C:\a\b\c\", @"C:\a\b\", @"..")]
[InlineData(@"C:\a\b\c\", @"C:\a", @"..\..")]
[InlineData(@"C:\a\b\c\", @"C:\a\", @"..\..")]
[InlineData(@"C:\a\", @"C:\b", @"..\b")]
[InlineData(@"C:\a", @"C:\a\b", @"b")]
[InlineData(@"C:\a", @"C:\A\b", @"b")]
[InlineData(@"C:\a", @"C:\b\c", @"..\b\c")]
[InlineData(@"C:\a\", @"C:\a\b", @"b")]
[InlineData(@"C:\", @"D:\", @"D:\")]
[InlineData(@"C:\", @"D:\b", @"D:\b")]
[InlineData(@"C:\", @"D:\b\", @"D:\b\")]
[InlineData(@"C:\a", @"D:\b", @"D:\b")]
[InlineData(@"C:\a\", @"D:\b", @"D:\b")]
[InlineData(@"C:\ab", @"C:\a", @"..\a")]
[InlineData(@"C:\a", @"C:\ab", @"..\ab")]
[InlineData(@"C:\", @"\\LOCALHOST\Share\b", @"\\LOCALHOST\Share\b")]
[InlineData(@"\\LOCALHOST\Share\a", @"\\LOCALHOST\Share\b", @"..\b")]
//[PlatformSpecific(TestPlatforms.Windows)] // Tests Windows-specific paths
public static void GetRelativePath_Windows(string relativeTo, string path, string expected) {
string result = PathNetCore.GetRelativePath(relativeTo, path);
Assert.Equal(expected, result);
// Check that we get the equivalent path when the result is combined with the sources
Assert.Equal(
Path.GetFullPath(path).TrimEnd(Path.DirectorySeparatorChar),
Path.GetFullPath(Path.Combine(Path.GetFullPath(relativeTo), result))
.TrimEnd(Path.DirectorySeparatorChar),
ignoreCase: true,
ignoreLineEndingDifferences: false,
ignoreWhiteSpaceDifferences: false);
}
}
}