c++ - 迭代器，循环导致段错误!为什么循环太多了？

Question

下面的代码循环了太多次，我不明白为什么。我环顾四周，还没有看到完全像这样的案例。我对迭代器还很陌生，所以这里可能有些简单的东西。感谢您的帮助!并希望对此的回应在未来对其他人有所帮助。

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，但是正如您从下面的输出中看到的那样，我正在迭代的 map 的大小是 2，那为什么它要循环第三次呢!

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(private)变量。在我看来它不会导致错误，除非有明显的我不知道的事情。

Answer 1

here is what return contents does.

这就是你的错误。 returnContents 函数返回 map 的拷贝。然后，您在它的两个不同拷贝上调用 begin 和 end。

要么返回一个(常量)引用:

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

或创建本地拷贝:

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