C++：如何解决在未知点引起的第一次机会异常？

Question

我正在处理的 C++ 项目在抛出第一次机会异常时终止。当我第一次尝试访问包含单个键值对的map<pair<int,int>, int> 时，这发生在调试模式下的 Visual Studio 2008 中。代码逻辑上没有错。

我已经阅读了第一次机会异常并了解它们可能并不总是有问题。尽管如此，我尝试打破所有此类异常，并且正如预期的那样发现生成了几个不会导致任何问题。

我正在处理的类非常大，并且包含许多自定义内存分配。我推测其中之一是导致问题的原因。然而，我花了几个小时试图找到一种方法来找出问题所在，但一直无法做到。

下面列出了第一次机会异常输出。这不是很有帮助！

First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x762cd09c in theapp.exe: 0xC0000005: Access violation reading location 0x6c696d00.
First-chance exception at 0x0050ae33 in theapp.exe: 0xC0000005: Access violation reading location 0x00000010.
Unhandled exception at 0x0050ae33 in theapp.exe: 0xC0000005: Access violation reading location 0x00000010.

在这一点上我真的很挣扎，不知道如何继续。

谁能建议我如何解决这个问题，并准确找出问题所在？非常感谢您的建议。

更新

这是相关代码。调试器在嵌套 FOR 中列出的第一个 cout 语句处中断：

        // Inside operator() :

        map<pair<int,int>,int> resultIdByStructIds;
        pair<int,int> spair (-1,-1); // Structure pair ids reusable reference.

        int nextMapEntryId = 0;
        int nextNumCandidates = 0;
        // For each remaining candidate.
        for (int ci = 0; ci < numCandidates; ) {
            // If candidate has been mapped or found not viable this mapping round,
            // move past it.
            if (candidatesDoneThisRound[ci] == currentMappingRoundId) {
                ++ci;
                continue;
            }

            Candidate candidate = candidates[ci];
            const int tId = candidate.tVertexId;
            const int pId = candidate.pVertexId;

            // Grab the result for this structure pair.
            // Create it if it doesn't exist.
            // Avoid copying as slight optimisation; simply
            // store pointer to true result instead.
            spair.first = tInfos[tId].structure->id;
            spair.second = pInfos[pId].structure->id;

            // DEBUG
            cout << "resultIdByStructIds size: " << resultIdByStructIds.size() << endl;
            for (map<pair<int,int>,int>::const_iterator ids_id = resultIdByStructIds.begin(); ids_id != resultIdByStructIds.end(); ++ids_id) {
                cout << ids_id->first.first << endl; // * Debugger breaks here.
                cout << ids_id->first.second << endl;
                cout << ids_id->second << endl;
                printf("Structures(%i,%i) => %i\n",ids_id->first.first,ids_id->first.second,ids_id->second);
            }
            //

            // code continues...

更新 2

这是相关地图的鼠标悬停描述图片；正如 Michael Burr 所建议的那样，它似乎已损坏。

Answer 1

一般来说，要查明应用程序崩溃的代码点，您可以在 Debug/Exceptions 下打开异常处理。在这种情况下，您将展开最后一个分支并检查访问冲突。当然，这将停止所有访问违规，而不仅仅是坏的（访问 0x10）。您可以通过在最后一个已知时刻打开陷阱来最小化这种情况。

通常您会发现一些内存使用错误。确定此类错误原因的最简单方法是使用第三方工具，例如 BoundChecker，一旦您损坏了内存，它就会对您大喊大叫。缺乏这一点，Raymond Chen 的建议是正确的。找出错误的对象，并使用监视窗口查看它何时更改。或者更有效的是，使用数据断点功能让程序在特定地址的数据发生变化时停止。