这段代码怎么可能:"ArgumentOutOfRangeException:startIndex不能大于字符串的长度"？

Question

我的C#代码中有以下方法:

/// <summary>
/// Removes the first (leftmost) occurence of a <paramref name="substring"/> from a <paramref name="string"/>.
/// </summary>
/// <param name="string">The string to remove the <paramref name="substring"/> from. Cannot be <c>null</c>.</param>
/// <param name="substring">The substring to look for and remove from the <paramref name="string"/>. Cannot be <c>null</c>.</param>
/// <returns>
/// The rest of the <paramref name="string"/>, after the first (leftmost) occurence of the <paramref name="substring"/> in it (if any) has been removed.
/// </returns>
/// <remarks>
/// <list type="bullet">
/// <item>If the <paramref name="substring"/> does not occur within the <paramref name="string"/>, the <paramref name="string"/> is returned intact.</item>
/// <item>If the <paramref name="substring"/> has exactly one occurence within the <paramref name="string"/>, that occurence is removed, and the rest of the <paramref name="string"/> is returned.</item>
/// <item>If the <paramref name="substring"/> has several occurences within the <paramref name="substring"/>, the first (leftmost) occurence is removed, and the rest of the <paramref name="string"/> is returned.</item>
/// </list>
/// </remarks>
/// <exception cref="ArgumentNullException">
/// The <paramref name="string"/> is <c>null</c>. -or- The <paramref name="substring"/> is <c>null</c>.
/// </exception>
public static string RemoveSubstring(string @string, string substring)
{
    if (@string == null)
        throw new ArgumentNullException("string");

    if (substring == null)
        throw new ArgumentNullException("substring");

    var index = @string.IndexOf(substring);
    return index == -1
        ? @string
        : @string.Substring(0, index) + @string.Substring(index + substring.Length);
}

实现看起来非常简单明了,单元测试具有很好的覆盖率.我的计算机,构建服务器或我有权访问的任何其他计算机或大多数生产环境中都没有出现意外结果.

除了只有一个远程客户偶尔使用以下堆栈跟踪报告此方法的应用程序崩溃:

System.ArgumentOutOfRangeException: startIndex cannot be larger than length of string.  
Parameter name: startIndex   
   at System.String.InternalSubStringWithChecks(Int32 startIndex, Int32 length, Boolean fAlwaysCopy)  
   at System.String.Substring(Int32 startIndex)
   at MyNamespace.StringUtils.RemoveSubstring(String string, String substring)
   at ...

遗憾的是,我无法远程访问此生产环境或其数据或任何其他信息.由于某些原因,目前我无法在那里部署日志系统或崩溃转储集合.

查看代码,并尝试不同的参数组合,我无法想象这个异常是如何发生的.

你能帮我一些想法吗？

Answer 1

RemoveSubstring("A", "A\uFFFD"); // throws ArgumentOutOfRangeException
RemoveSubstring("A", "A\u0640"); // throws ArgumentOutOfRangeException

用于.NET中字符串操作的许多函数,包括IndexOf默认情况下特定于文化的(通常存在可以传递StringComparison.Ordinal或StringComparer.Ordinal切换到按位比较的重载).就个人而言,我对选择的默认行为并不十分满意,但对它做任何事情都为时已晚,除非可能设置明确的开发指南和FxCop规则.

但有时特定于文化的操作正是您所需要的.不幸的是,它们的语义可能很棘手且反直觉,可能会违反一些通常假定的不变量,并且需要处理很多极端情况.负责在应用程序中实现文化敏感逻辑的开发人员应该在这方面非常合格,并且始终能够准确理解他们正在做什么.我建议将此区域的审查和测试标准设置为高于正常水平.