title: "operator bool 函数"
date: 2023-08-14T16:05:25+08:00
tags: ["C++"]
categories: []
draft: false

参考文档

user-defined conversion function - cppreference.com
The Safe Bool Idiom - 知乎

为什么`operator bool()`需要用explicit修饰?

c++ - Why does declaring an operator bool() const member overload the [] operator? - Stack Overflow

The operator is coming from the built-in subscript operator which treats expressions A[B] as *(A + B).
This results in the evaluation of *(1 + "wut") => 'u', which then causes the if condition to pass, as 'u' is a non-zero value.
Declare your member as explicit operator bool() to prevent your type from being implicitly converted to other integral types.

#include <iostream>
using namespace std;

struct Test {
    operator bool() const {
        return true;
    }
};

int main(int argc, char** argv) {
    Test test;

    if (test["wut"])
        cout << "Success (test[\"wut\"])\n";
}