c ++ 11结构初始化编译错误

问题描述

  struct SS {int a; int s;}; 
 
 int main（）
 {
 vector< SS> v; 
 v.push_back（SS {1，2}）; 
} 
  

代码可以编译时没有任何错误。但是，当结构在类中初始化时，我得到编译错误。任何人都可以解释一下？

  struct SS {int a = 0; int s = 2;}; 
  

错误：

 code>在函数'int main（）'：
错误：没有匹配的函数调用'SS :: SS（<大括号初始值列表>）'
 v.push_back SS {1，2}）; 
 ^ 
注意：候选项是：
注意：constexpr SS :: SS（）
 struct SS {int a = 0; int s = 2;}; 
 ^ 
注意：候选人期望有0个参数，2提供
注意：constexpr SS :: SS（const SS&）
注意：候选人期望1个参数，2提供
注意：constexpr SS :: SS（SS&&）
注意：候选人期望1个参数，2提供
  

$ b

$ b

  struct SS {int a = 0; int s = 2;}; 
  

您将类设为非汇总。这意味着您不能再像这样初始化一个实例：

  SS s {1,2}; 
  

要使此初始化语法适用于非聚合，您必须添加一个双参数构造函数：

  struct SS 
 {
 SS（int a，int s） ，s（s）{} 
 int a = 0; 
 int s = 2; 
}; 
  

此限制已在C ++ 14中取消。

注意，你可能想为类添加一个默认构造函数。用户提供的构造函数的存在会禁止编译器生成默认的构造函数。

参阅相关阅读。

struct SS {int a; int s;};

int main ()
{
   vector<SS> v;
   v.push_back(SS{1, 2});
}

The code can be compiled without any error. However, when the struct is initialized in class, I got compilation error. Can anyone explain it?

struct SS {int a = 0; int s = 2;};

Error:

In function ‘int main()’:
error: no matching function for call to ‘SS::SS(<brace-enclosed initializer list>)’
     v.push_back(SS{1, 2});
                        ^
note: candidates are:
note: constexpr SS::SS()
 struct SS {int a = 0; int s = 2;};
        ^
note:   candidate expects 0 arguments, 2 provided
note: constexpr SS::SS(const SS&)
note:   candidate expects 1 argument, 2 provided
note: constexpr SS::SS(SS&&)
note:   candidate expects 1 argument, 2 provided

解决方案

In C++11, when you use non static data member initialization at the point of declaration like you do here:

struct SS {int a = 0; int s = 2;};

you make the class a non-aggregate. This means you can no longer initialize an instance like this:

SS s{1,2};

To make this initialization syntax work for a non-aggregate, you would have to add a two-parameter constructor:

struct SS
{
  SS(int a, int s) : a(a), s(s) {}
  int a = 0;
  int s = 2;
};

This restriction has been lifted in C++14.

Note that you may want to add a default constructor for the class. The presence of a user-provided constructor inhibits the compiler generated default one.

See related reading here.

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