扩展在if / else序列中初始化的变量的范围 [英] Expand scope of a variable initialized in a if/else sequence
问题描述
我正在写一段代码,其中我想根据条件使用一个类的不同构造函数。到目前为止,我使用 if
和 else
语句来构造对象,但是实例被'
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.
以下是代码中的样子:
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
尝试使用 static
关键字到目前为止没有成功。是否有一种常见的有条件使用不同构造函数的方法,而不必重新定义构造函数?
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
>
try the following :)
MyClass my_object = my_boolean ? MyClass(arg1) : MyClass(arg1,arg2);
考虑到这个代码会工作,即使该类没有默认构造函数。
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;
}
我已获得以下输出
p.x = 1, p.y = 2
你得到了什么输出? :)
What output have you gotten? :)
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