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      1. 返回临时对象并绑定到 const 引用

        时间:2023-12-03

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                  本文介绍了返回临时对象并绑定到 const 引用的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着跟版网的小编来一起学习吧!

                  问题描述

                  可能的重复:
                  const 引用是否会延长临时引用的寿命?

                  我的编译器不会抱怨将临时分配给 const 引用:

                  My compiler doesn't complain about assigning temporary to const reference:

                  string foo() {
                    return string("123");
                  };
                  
                  int main() {
                    const string& val = foo();
                    printf("%s
                  ", val.c_str());
                    return 0;
                  }
                  

                  为什么?我认为从 foo 返回的字符串是临时的,val 可以指向生命周期已经结束的对象.C++ 标准是否允许这样做并延长返回对象的生命周期?

                  Why? I thought that string returned from foo is temporary and val can point to object which lifetime has finished. Does C++ standard allow this and prolongs the lifetime of returned object?

                  推荐答案

                  这是一个 C++ 特性.该代码是有效的,并且完全符合它的功能.

                  This is a C++ feature. The code is valid and does exactly what it appears to do.

                  通常,临时对象仅持续到它出现的完整表达式的结尾.但是,C++ 特意指定将临时对象绑定到堆栈上对 const 的引用会将临时对象的生命周期延长至引用本身的生命周期,从而避免常见的悬空引用错误.在上面的例子中, foo() 返回的临时值一直存在到右花括号为止.

                  Normally, a temporary object lasts only until the end of the full expression in which it appears. However, C++ deliberately specifies that binding a temporary object to a reference to const on the stack lengthens the lifetime of the temporary to the lifetime of the reference itself, and thus avoids what would otherwise be a common dangling-reference error. In the example above, the temporary returned by foo() lives until the closing curly brace.

                  P.S:这仅适用于基于堆栈的引用.它不适用于作为对象成员的引用.

                  P.S: This only applies to stack-based references. It doesn’t work for references that are members of objects.

                  全文:GotW #88:AHerb Sutter 的最重要的常量"候选者.

                  这篇关于返回临时对象并绑定到 const 引用的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持跟版网!

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