std::stack 如何强制容器 class 满足某些要求

Question

如果您使用不满足所需底层容器要求的容器创建 stack，则会出现编译错误。这是一个可以在编译时与运行时确定的错误。

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;
}

请问return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;
                                                             ^~~~~~~~~

我希望能够强制执行模板类型的要求，我希望使用 std::stack 的做法作为参考。

Answer 1

std::stack 实际上并没有做任何事情。 std::stack里面有一个like like

using value_type = Container::value_type;

对于你的情况，Container 是 Test 并且由于 Test::value_type 不存在，你会得到一个编译器错误。

std::stack 如何强制容器 class 满足某些要求

How does std::stack enforce that the container class meets certain requirements

c++

stack

std