c++ - 使用 std::list 时 std::string 的内存泄漏

Question

我正在使用 std::list<std::string>在我目前的项目中。但是与此相关的某个地方存在内存泄漏。所以我单独测试了有问题的代码:

#include <iostream>
#include <string>
#include <list>

class Line {
public:
    Line();
    ~Line();
    std::string* mString;
};

Line::Line() {
    mString = new std::string("XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX");
}

Line::~Line() {
    //mString->clear(); // should not be neccessary
    delete mString;
}

int main(int argc, char** argv)
{
    // no memory leak
    while (1==1) {
        std::string *test = new std::string("XXXXXXXXXXXXXXXXXXXXXXXX");
        delete test;
    }

    // LEAK!
    // This causes a memory overflow, because the string thats added
    // to the list is not deleted when the list is deleted.
    while (1==1) {
        std::list<std::string> *sl = new std::list<std::string>;
        std::string *s = new std::string("XXXXXXXXXXXXXXXXXXXXXXX");
        sl->push_back(*s);
        //sl->pop_back(); //doesn't delete the string?- just the pointer
        delete sl;
    }

    // LEAK!
    // Here the string IS deleted, but the memory does still fill up
    // but slower
    while (1==1) {
        std::list<Line> *sl = new std::list<Line>;
        Line *s = new Line();
        sl->push_back(*s);
        //sl->pop_back(); //does delete the Line-Element
        sl->clear();
        delete sl;
    }
    return 0;

    // this does not cause any noticable memory leak
    while (1==1) {
        std::list<int> *sl = new std::list<int>;
        int i = 0xFFFF;
        sl->push_back(i);
        sl->clear();
        delete sl;
    }
    return 0;

    // This does not cause any overflow or leak
    while (1==1) {
        int *i;
        i= new int [9999];
        delete[] i;
    }

}

为什么我的字符串列表会导致内存泄漏？删除列表不应该导致在每个包含的字符串上调用析构函数吗？

Answer 1

在第一种情况下，list class 不知道您使用 new 分配了字符串，并且无法删除它。特别是，该列表只包含您传入的字符串的拷贝。

同样，在第二种情况下，您永远不会释放行对象 s，因此会泄漏内存。删除内部字符串的原因是您没有正确实现复制构造函数。因此，如果你复制一个 Line 对象，它们都会引用同一个字符串指针，如果你试图删除它们，你就有麻烦了。