重载delete []具有特定参数的运算符

问题描述

我们试图重载带有特定参数的delete []运算符。哪个是正确的方法调用它？我们使用GNU编译器并获取所有这些样本的编译器错误：

We're trying to overload the delete[] operator with specific arguments. Which is the right way to call it? We use the GNU compiler and obtain compiler errors with all of these samples:

#include<memory>
using namespace std;
typedef unsigned int P;

struct A{
    static allocator<A>m;
    P p;
    void*operator new[](size_t s){return m.allocate(s);}
    void operator delete[](void*p,int s){m.deallocate((A*)p,s);}
    void operator delete[](void*p,size_t t,int s){m.deallocate((A*)p,s);}
};

int main(){
    A*a=new A[10];
    //delete (5) []a;       //expected ',' before 'a'
    //delete[5]a;           //expected ';' before ']' token
    //delete[] (5) a;       //type ‘int’ argument given to ‘delete’, expected
    //delete[]a (5);        //a’ cannot be used as a function
    //delete[]((int)5)a;    //type ‘int’ argument given to ‘delete’, expected pointer
    //delete[]a((int)5);    //‘a’ cannot be used as a function
    return 0;
}

推荐答案

对于这种放置删除器。

只有当位置为new的构造函数抛出异常时，才会调用放置删除器（与您声明的位置相同）。

然后程序将调用匹配的布置删除器（相同的签名），并尝试释放自定义分配的内存。

There's no "syntactic sugar" for this kind of placement deleter.
A placement deleter (like what you've declared) is only called when a constructor that was called by a placement new, throws an exception.
Then the program will call the matching placement deleter (same signature) and try to free the customly allocated memory.

如果您仍然想调用此方法，手动调用操作符：

If you still want to call this method, you'll have to call the operator manually:

A::operator delete[](a, 5);

这里有一个很好的例子：

There's a nice example of how it works here: http://en.cppreference.com/w/cpp/memory/new/operator_delete

请注意类析构函数中的异常（在触发异常后调用delete操作符）：

Notice the exception in the class destructor (the delete operator is called after the exception is triggered):

#include <stdexcept>
#include <iostream>
struct X {
    X() { throw std::runtime_error(""); }
    // custom placement new
    static void* operator new(std::size_t sz, bool b) {
        std::cout << "custom placement new called, b = " << b << '\n';
        return ::operator new(sz);
    }
    // custom placement delete
    static void operator delete(void* ptr, bool b)
    {
        std::cout << "custom placement delete called, b = " << b << '\n';
        ::operator delete(ptr);
    }
};
int main() {
   try {
     X* p1 = new (true) X;
   } catch(const std::exception&) { }
}

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