函数调用中的新运算符 [英] new operator in function call

问题描述

我的问题是在函数调用内用new运算符分配的对象会发生什么情况.

My question is what happens to the object allocated with the new operator that is inside a function call.

一个具体的例子:我有一个私有向量pV，我想将其发送到类foo->func(std::vector<int> *vec)之外的对象/函数.我首先尝试写

A specific example: I have a private vector pV which I want to send to a object/function outside of the class, foo->func(std::vector<int> *vec). I first tried to write

foo->func( new std::vector<int>(pV) )

但这会导致内存泄漏(当在循环内重复调用该函数时).当我专门创建一个新对象(称为函数)，然后删除该对象时，整个过程正常进行，而没有内存泄漏.

but this resulted in a memory leak (when said function is called repeatedly inside a loop). When I specifically created a new object, called the function and then deleted that object, the whole thing worked, without the memory leak.

新创建的对象'expire'不会在函数返回时被删除吗?如果没有，应该如何从调用的函数内部删除对象?哪种方法更好?

Shouldn't the newly created object 'expire' and be deleted when the function returns? If not, how should I delete the object, from inside the called function? And which is the better approach?

推荐答案

用delete分配的对象最终必须用delete释放，否则会发生泄漏. new的分配与函数调用无关-您可以在一个函数中使用new创建内容，然后在另一个函数中使用delete释放内容，而不会出现问题.

Objects allocated with new must eventually be freed with delete, or there will be leaks. Allocation with new is independent of function calls - you can create something with new in one function and free it with delete in another without problems.

如果要在函数中分配并在函数退出时释放对象，请执行以下操作:

If you want an object that is allocated in a function and freed when the function exits, just do this:

void foo(...) {
    // some code

    MyClass myobj(...); // object allocated here
    // some more code
    return; // object freed here (or whenever function exits)
}

如果您需要将 pointer 传递给函数的对象，则无需为此使用new.您可以使用&运算符:

If you need to pass a pointer to your object to a function, you needn't use new for that either; you can use the & operator:

std::vector<int> myvec(pV);
foo->func(&myvec);

在这种情况下，myobj是一个自动变量，放置在堆栈中，并在函数退出时自动删除.在这种情况下，无需使用new.

In this case myobj is an automatic variable which is placed on the stack and automatically deleted when the function exits. There is no need to use new in this case.

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