c++ – Unbenannter Namespace kann nicht in .h platziert werden

Question

Unbenannter Namespace kann nicht in .h platziert werden. Können Sie ein Beispiel nennen, warum dies nicht zulässig ist?
Nach langem Überlegen habe ich keine Beispiele gefunden.

Answer 1

关键看怎么用，在unnamed namespace中放什么东西，一个例子，如果放变量，就有问题了。

//one.h
#include <iostream>
#include <typeinfo>

namespace {
class TestClass {
};
int i;
}

const std::type_info& one_get_TestClass_Info();
const std::type_info& two_get_TestClass_Info();

//one.cpp
#include "one.h"
const std::type_info& one_get_TestClass_Info()
{
    i = 10;
    std::cout << "val: " << i << "   addr: " << &i << std::endl;
    return typeid(TestClass);
}

//two.cpp
#include "one.h"
#include <iostream>
#include <typeinfo>
using namespace std;

const std::type_info& two_get_TestClass_Info()
{
    std::cout << "val: " << i << "   addr: " << &i << std::endl;
    return typeid(TestClass);
}
//main.cpp

#include "one.h"
using namespace std;

int main()
{
    const std::type_info& t1 = one_get_TestClass_Info();
    const std::type_info& t2 = two_get_TestClass_Info();
    std::cout << "one has type: " << t1.name() << '\n'
              << "two has type: " << t2.name() << '\n';
    if (t1 == t2) {
        cout << "same type";
    }

    return 0;
}

输出为：

val: 10   addr: 0x602200
val: 0   addr: 0x602208
one has type: N12_GLOBAL__N_19TestClassE
two has type: N12_GLOBAL__N_19TestClassE

稍微详细点，看这里 : https://zsounder.github.io/20...。