C++复习Lvalues,Rvalues,References

最新推荐文章于 2022-12-15 17:27:48 发布

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本文详细介绍了C++11中lvalue引用和rvalue引用的概念及其用法。通过实例展示了如何利用引用避免对象复制，提高程序效率。同时，文章还探讨了在函数声明和返回值中使用引用的语法。

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An lvalue is an expression that identifies a non-temporary object. An rvalue is an expression that identifies a temporary object or is a value (such as a literal constant) not associated with any object. As a general rule, if you have a name for a variable, it is an lvalue, regardless of wherther it is modifiable.

In C++11, we can have two types of references: lvalue references and rvalue references.

In c++11, an lvalue reference is declared by placing an & after some type. An lvalue reference then becomes a synonym(i.e.,another name)for the object it references.

In C++11,an rvalue reference is declared by placing an && after some type. An rvalue reference has the same characteristics as an lvalue reference except that. inlike an lvalue reference, an rvalue reference can also reference an rvalue(i.e.. a temporary).

lvalue references use

aliasing complicated names.///copy. auto & whichList = theLists[ myhash( x , theLists.size())];
range for loops.////for(auto & x: arr) ++x;
avoiding a copy.///auto &x=findMax(arr);///if auto is not used. the typically a non-modifiable reference is explicitly stated with const;

This code illustrates two important concepts:

Reference variables are often used to avoid copying objects avoid copying objects across function-call boundaries(either in the function call or the function return).
Syntax is needed in function declarations and returns to enable the passing and returning using references instead of copies.
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