C ++中临时变量的用途是什么 [英] What is the use of temporaries in c++

问题描述

朋友，

我对C ++中的临时功能有些怀疑.
我并不完全理解临时工的概念.我已经在google中搜索过，但是对此却没有任何令人满意的解释，最重要的是我们为什么使用它?所以，伙计们，请允许我给出一些很好的解释，并举例说明我很容易理解.

...等待您的回复...



问候.
Johny ...

Hi Friends,

I have some doubt in temporaries in C++.
I did not exactly understand the concept of temporaries. I already searched in google, but I did not get any satisfactory explanation of this and most importantly why we use this? So guys please let me give some good explanation with example for that i can understand easily.

...Waiting for your replies...



Regards.
Johny...

推荐答案

一种简单的调整"方法是考虑如何计算类似
的表达式

A simple way to "tune" on them is thinking on how compute an expression like

z = (a+b)*c;

c乘以什么?
"a+b的结果"，但是它必须作为+的结果以某种方式存储，仅用于*进行计算的时间.

现在呢

What does multiply c?
"The result of a+b", but it has to be stored somehow as result of + just for the time neede to * to compute.

Now what about

z = operator*(operator+(a,b),c);

这与上面的相同:名为"operator+"的函数返回结果，
然后将其以临时值的形式传递给另一个函数-operator*(在这种情况下).

很像
z = f(g(a,b),c);

表示为

This is the same as above: the function named "operator+" return a result,
that is then passed to another function - operator*, in this case - in the form of a temporary value.

Much like
z = f(g(a,b),c);

expressed as

tmp = g(a,b);
z = f(tmp,c);

当然，这对临时对象不是完全详尽无遗，只是在必须存在临时对象的情况下对其进行想象.

Of course, this is not completely exhaustive about temporaries, but is just a way to imagine them in a case they have to come to existence.

临时对象称为rvalues，非临时对象称为rvalues左值.代码中的命名对象是左值，而作为(子)表达式结果的临时对象是临时对象-右值.例如(x + y)是一个右值，而(x)是一个左值.每个表达式都是左值或右值.您可以轻松地在两者之间进行区分:您无法获得指向右值的指针，因此在使用& x进行操作时无法说&(x + y). C ++ 11引入了一个非常酷的功能，即rvalue参考，可以更有效地处理临时对象.要阅读有关临时人员和C ++ 11的新功能的信息，请阅读这篇冗长但精湛的说明文章:

Temporaries are called rvalues and non-temporaries are called lvalues. Named objects in your code are lvalues, and temporary object that are the results of your (sub)expressions are temporary objects - rvalues. For example (x+y) is an rvalue and (x) is an lvalue. Every expression is either an lvalue or rvalue. You can easily distinguis between the two: you can not get a pointer to an rvalue so you can not say &(x+y) while you can do this with &x. The C++11 introduces a very cool feature to handle temporaries more efficiently, its the rvalue reference. To read about temporaries and this new C++11 feature read this lengthy but superb explaining article: http://blogs.msdn.com/b/vcblog/archive/2009/02/03/rvalue-references-c-0x-features-in-vc10-part-2.aspx[^]

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