C ++ 11中的std :: vector< bool> :: emplace [英] std::vector<bool>::emplace in C++11
问题描述
根据 cppreference.com :
注释
专业化 std: :vector< bool>
在C ++ 14之前没有 emplace()
成员
。
The specialization std::vector<bool>
did not have emplace()
member
until C++14.
是什么意思?模板专业化可以省略成员吗?是否意味着根本不存在成员功能?还是只是不专业?
What does it mean? Can template specialization omit member? Does mean that member function is not present at all? Or is it just not specialized?
以下代码似乎适用于gcc 7.1.0:
Following code seems to work on gcc 7.1.0:
#include <iostream>
#include <vector>
using namespace std;
int main()
{
std::vector<bool> v;
v.emplace_back(true);
v.emplace_back(false);
for (const auto &b : v) {
std::cout << b << std::endl;
}
}
http://coliru.stacked-crooked.com/a/07c8c0fc6050968f
推荐答案
模板专业化可以与通用模板完全不同。因此,从理论上讲,您不知道类 A< int>
和 A< bool>
是否具有任何公共成员:
A template specialization can be completely different from the generic template. So in theory, you cannot know whether the classes A<int>
and A<bool>
have any common members:
template <typename T>
class A
{
public:
void foo()
{}
};
template <>
class A<bool>
{
public:
void bar()
{}
};
int main()
{
A<int> a;
a.foo();
A<bool> b;
b.bar();
b.foo(); // error: 'class A<bool>' has no member named 'foo'
}
类 std :: vector< bool>
是一个专门的模板。您在标准中的引用表明,在C ++ 14之前,该专业化中缺少 emplace()
方法。
The class std::vector<bool>
is a specialized template. Your quote from the standard says that the emplace()
method was missing in that specialization until C++14.
实际上,像libstdc ++这样的具体标准库可能已经为 std :: vector< bool> $ c $提供了
emplace()
方法。 c>甚至在C ++ 14之前,但在标准中并不是必需的。
In practice, concrete standard libraries such as libstdc++ may have provided the emplace()
method for std::vector<bool>
even before C++14, but it was not required in the standard.
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