在c ++中初始化对象之前声明对象 [英] Declaring an object before initializing it in c++

问题描述

是否可以在c ++中声明一个变量而不实例化它？我想做这样的事情：

  
 if（happyDay（））
 a（puppies）; // constructor call 
 else 
 a（toads）; 
  

基本上，我只想声明一个外部的条件，所以它获得正确的范围。 p>

有没有办法做到这一点，不使用指针和在堆上分配 a ？

$ p

解决方案

你不能直接在C ++中做到这一点，因为当你定义对象时默认构造函数。

但是，您可以运行一个参数化构造函数以开头：

  Animal a（getAppropriateString（））; 
  

或者你实际上可以使用 ?:运算符确定正确的字符串。
（更新：@Greg给出了这个的语法，看到这个答案）

Is it possible to declare a variable in c++ without instantiating it? I want to do something like this:

Animal a;
if( happyDay() ) 
    a( "puppies" ); //constructor call
else
    a( "toads" );

Basially, I just want to declare a outside of the conditional so it gets the right scope.

Is there any way to do this without using pointers and allocating a on the heap? Maybe something clever with references?

解决方案

You can't do this directly in C++ since the object is constructed when you define it with the default constructor.

You could, however, run a parameterized constructor to begin with:

Animal a(getAppropriateString());

Or you could actually use something like the ?: operator to determine the correct string. (Update: @Greg gave the syntax for this. See that answer)

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