扩展在 if/else 序列中初始化的变量的范围

2022-01-04 00:00:00 scope c++

我正在编写一段代码，其中我想根据条件使用类的不同构造函数.到目前为止，我已经使用 if 和 else 语句来构造对象，但该实例随后被困"在括号中，无法在代码中进一步使用.

I'm writing a piece of code in which I'd like to use a different constructor of a class depending on a condition. So far I've used if and else statements to construct the object, but the instance is then 'trapped' in the brackets and can't be used further in the code.

代码如下:

if (my_boolean){
    MyClass my_object(arg1); //calling a first constructor
}
else {
    MyClass my_object(arg1,arg2); //calling another constructor
}
//more code using my_object

到目前为止，我尝试使用 static 关键字但没有成功.有条件地使用不同的构造函数而不必重新定义构造函数的通用方法吗?

I tried using the static keyword without success so far. Is there a common way of conditionally using different constructors without having to redefine the constructors?

推荐答案

请尝试以下操作:)

MyClass my_object = my_boolean ? MyClass(arg1) : MyClass(arg1,arg2);

考虑到即使类没有默认构造函数，这段代码也能工作.

Take into account that this code will work even if the class has no default constructor.

这是一个示范性的例子

#include <iostream> 
#include <cstdlib>
#include <ctime>

int main () 
{
    struct Point
    {
        Point( int x ) : x( x ) {}
        Point( int x, int y ) : x( x ), y( y ) {}
        int x = 0;
        int y = 0;
    };

    std::srand( ( unsigned )std::time( 0 ) );

    Point p = std::rand() % 2 ? Point( 1 ) : Point( 1, 2 );

    std::cout << "p.x = " << p.x << ", p.y = " << p.y << std::endl;  

    return 0; 
}

我得到了以下输出

p.x = 1, p.y = 2

你得到了什么输出?:)

What output have you gotten? :)

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