当类成员涉及c ++ 11时如何使用自动返回和decltype？ [英] How to use auto return and decltype when class members involved with c++11?

问题描述

例如

  struct A 
 {
 auto count（） - > decltype（m_count）{return m_count; } 
 int m_count; 
}; 
  

上述获取编译错误，因为m_count在 decltype 无法识别。如何解决它？ auto 返回并从 m_count 获取类型。

订单更改时代码会编译

  struct A 
 {
 int m_count; 
 auto count（） - > decltype（m_count）{return m_count; } 
}; 
  

但是如何让第一种情况下工作？

decltype 中声明的名称。 code>用于尾随返回类型。因此，您必须重新排序您的声明：

  struct A 
 {
 int m_count; 
 auto count（） - > decltype（m_count）{return m_count; } 
}; 
  

For example

struct A
{
    auto count() -> decltype(m_count) { return m_count; }
    int m_count;        
};

The above gets compilation error because m_count in decltype is not recognized. How to work around it? auto return and get the type from m_count must be used.

The code compiles when the order is changed

struct A
{
    int m_count;        
    auto count() -> decltype(m_count) { return m_count; }
};

but how do I get the first case to work?

解决方案

In C++, you can't use a name that hasn't been introduced (declared) in a declaration, including in a decltype for a trailing return type. So you must reorder your declarations :

struct A
{
    int m_count;
    auto count() -> decltype(m_count) { return m_count; }
};

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