C ++，是否可以直接调用构造函数而无需new? [英] C++, is it possible to call a constructor directly, without new?

问题描述

如果我已经有对象的内存，我可以不使用 new 显式调用构造函数吗?

Can I call constructor explicitly, without using new, if I already have a memory for object?

class Object1{
    char *str;
public:
    Object1(char*str1){
        str=strdup(str1);
        puts("ctor");
        puts(str);
    }
    ~Object1(){
        puts("dtor");
        puts(str);
        free(str);
    }
};

Object1 ooo[2] = {
     Object1("I'm the first object"), Object1("I'm the 2nd")
};

do_smth_useful(ooo);
ooo[0].~Object1(); // call destructor
ooo[0].Object1("I'm the 3rd object in place of first"); // ???? - reuse memory

推荐答案

排序.您可以使用 placement new 使用已分配的内存运行构造函数:

Sort of. You can use placement new to run the constructor using already-allocated memory:

 #include <new>

 Object1 ooo[2] = {Object1("I'm the first object"), Object1("I'm the 2nd")};
 do_smth_useful(ooo);
 ooo[0].~Object1(); // call destructor

 new (&ooo[0]) Object1("I'm the 3rd object in place of first");

因此，您仍在使用 new 关键字，但不会进行内存分配.

So, you're still using the new keyword, but no memory allocation takes place.

这篇关于C ++，是否可以直接调用构造函数而无需new?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！