Question

下面的代码经历了很多次循环，我很困惑为什么。我环顾四周，并没有看到完全像这样的情况。我对迭代器很新，所以这里可能有些简单。感谢您的帮助！希望对此的回应可以帮助其他人。

std::multimap<std::string,std::vector<Token> >::iterator end = theFacts.returnContents().end();
for (mapITER = theFacts.returnContents().begin() ; mapITER != end; mapITER++) {

  cout << "ANOTHER ITERATION THROUGH FACTS" << endl;
  cout << mapITER->first << endl;
  cout << contents.begin()->first << endl;

  if (mapITER->first == contents.begin()->first) {

    cout << "same scheem type so I keep going!" << endl;

    bool successfull = true;

    cout << "starting to seek match --> size --> " << mapITER->second.size() << endl;

    for (int x = 0; x< mapITER->second.size(); x++) {

      std::cout << "processing! "
                << mapITER->second[x].getTokensValue() << "<<<<<<is equal?>>>>>>"
                << contents.begin()->second[x].getTokensValue() << std::endl;

      if (mapITER->second[x].getTokensValue()
        == contents.begin()->second[x].getTokensValue()) {

        cout << "pushing value" << endl;
        newBaby.push_back(contents.begin()->second[x]);

      } else {

        cout << "failure" << endl;
        successfull = false;
      }
    }

    if (successfull) {

      std::cout << "match successfully found" << std::endl;

      if (returnme.contents.empty()) {

        returnme = Relation(contents.begin()->first, newBaby);
        cout << returnme.toString() << endl;

      } else {

        returnme.relationInsert(contents.begin()->first, newBaby);
        cout << returnme.toString() << endl;
      }

    } else {
      // Anser is NO
    }
  }
}

我知道我没有提供完整的代码，但是你可以看到形成以下输出，我正在迭代的地图的大小是2，所以为什么它第三次循环！

WHERE TO END --> size of maps (number of iterations that shoudl occure2
ANOTHER ITERATION THROUGH FACTS
snap
snap
same scheem type so I keep going!
starting to seek match --> size --> 4
processing! '12345'<<<<<<is equal?>>>>>>'67890'
failure
processing! 'Snoopy'<<<<<<is equal?>>>>>>'Van Pelt'
failure
processing! '12 Apple'<<<<<<is equal?>>>>>>'34 Pear'
failure
processing! '555-1234'<<<<<<is equal?>>>>>>'555-5678'
failure
ANOTHER ITERATION THROUGH FACTS
snap
snap
same scheem type so I keep going!
starting to seek match --> size --> 4
processing! '67890'<<<<<<is equal?>>>>>>'67890'
pushing value
processing! 'Van Pelt'<<<<<<is equal?>>>>>>'Van Pelt'
pushing value
processing! '34 Pear'<<<<<<is equal?>>>>>>'34 Pear'
pushing value
processing! '555-5678'<<<<<<is equal?>>>>>>'555-5678'
pushing value
match successfully found
PRINT RELATION CALLED 
snap('67890','Van Pelt','34 Pear','555-5678')
ANOTHER ITERATION THROUGH FACTS
Segmentation fault (core dumped)

这是返回内容的作用。

std::multimap<std::string,std::vector<Token> > Relation :: returnContents()
{
    return contents;
}

其中contents是Relation类中的私有变量。在我看来它不应该导致错误，除非有一些我不知道的明显事物。

Answer 1

这是返回内容的作用。

你有错误。函数returnContents返回地图的副本。然后，您可以在其中的两个不同副本上调用begin和end。

返回（const）引用：

const std::multimap<std::string,std::vector<Token> >& Relation::returnContents() {
    return contents;
}

或创建本地副本：

std::multimap<std::string,std::vector<Token> > tmp = theFacts.returnContents();
for (mapITER = tmp.begin() ; mapITER != tmp.end(); mapITER++) { ...

迭代器，循环导致seg故障！为什么循环过多？

1 个答案: