std::stack如何强制容器类满足某些要求?

Question

如果使用不满足所需底层容器要求的容器创建stack，则会得到编译错误。这是如何在编译时和运行时确定的错误?

例如:

#include <iostream>
#include <stack>
using namespace std;
class Test {
int data;
};
int main()
{
stack<int, Test> s;
// s.push(5);
cout<<"Hello World";
return 0;
}

将返回编译错误:

In file included from /usr/include/c++/6/stack:61:0,
from main.cpp:10:
/usr/include/c++/6/bits/stl_stack.h: In instantiation of ‘class std::stack<int, Test>’:
<span class="error_line" onclick="ide.gotoLine('main.cpp',20)">main.cpp:20:22</span>:   required from here
/usr/include/c++/6/bits/stl_stack.h:102:46: error: no type named ‘value_type’ in ‘class Test’
typedef typename _Sequence::value_type _Sequence_value_type;
^~~~~~~~~~~~~~~~~~~~
/usr/include/c++/6/bits/stl_stack.h:124:61: error: no type named ‘value_type’ in ‘class Test’
typedef typename _Sequence::value_type                value_type;
^~~~~~~~~~
/usr/include/c++/6/bits/stl_stack.h:125:61: error: no type named ‘reference’ in ‘class Test’
typedef typename _Sequence::reference                 reference;
^~~~~~~~~
/usr/include/c++/6/bits/stl_stack.h:126:61: error: no type named ‘const_reference’ in ‘class Test’
typedef typename _Sequence::const_reference           const_reference;
^~~~~~~~~~~~~~~
/usr/include/c++/6/bits/stl_stack.h:127:61: error: no type named ‘size_type’ in ‘class Test’
typedef typename _Sequence::size_type                 size_type;
^~~~~~~~~

我希望能够执行模板类型的需求，我希望使用std::stack如何作为参考。

Answer 1

std::stack实际上没有做任何事情。std::stack内部有一个like like

using value_type = Container::value_type;

和您的情况，Container是Test，因为Test::value_type不存在，你得到一个编译器错误。