【发布时间】：2014-04-15 07:08:43
【问题描述】：
下面的代码循环的次数太多了，我很困惑为什么。我环顾四周，并没有看到一个完全像这样的案例。我对迭代器相当陌生，所以这里可能有一些简单的东西。感谢您的帮助！希望对此的回应能在未来帮助其他人。
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，但是正如您从以下输出中看到的那样，我正在迭代的地图的大小是 2，那么为什么它会第三次循环！
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;
}
其中内容是 Relation 类中的私有变量。在我看来，这应该不会导致错误，除非有明显的我不知道。
【问题讨论】：
-
如果您展示了足够的代码来诊断问题会有所帮助，例如
end声明在哪里以及它的价值是什么？ -
end中的mapITER != end是什么？ -
在您的情况下尝试 mapITER != theFacts.end()。使用迭代器进行预增量会更好（您不需要复制对象）
-
猜测：
theFacts.returnContents()不返回引用。 -
我添加了 end 的实例化。当它通过循环额外（在本例中为第 3 次）并尝试拉 mapITER->first 时，它似乎出现了段错误。我不明白为什么它会第三次循环！
标签： c++ loops iterator segmentation-fault