在全局范围内声明它时发生命名空间错误

Question

我有3个文件Test.h,Test.cpp和main.cpp

Test.h

#ifndef Test_H
#define Test_H
 namespace v
{
    int g = 9;;
    }
class namespce
{
public:
    namespce(void);
public:
    ~namespce(void);
};
#endif

TEST.CPP

   #include "Test.h"


namespce::namespce(void)
{
}

namespce::~namespce(void)
{
}

Main.cpp的

#include <iostream>
using namespace std;
#include "Test.h"
//#include "namespce.h"


int main ()
{

    return 0;

}

在建设过程中出现以下错误..

1>namespce.obj : error LNK2005: "int v::g" (?g@v@@3HA) already defined in main.obj
1>C:\Users\E543925\Documents\Visual Studio 2005\Projects\viku\Debug\viku.exe : fatal error LNK1169: one or more multiply defined symbols found

请尽快帮助..

Answer 1

这是一个定义:

namespace v
{
    int g = 9;
}

由于每个文件中的重复main.obj和重复.包含防护仅在单个翻译单元中防止多个包含.test.obj#include "Test.h".cpp#ifndef Test_H

改成:

namespace v
{
    extern int g; // This is now a declaration and extern tells the compiler
                  // that there is definition for g somewhere else.
}

并将以下内容添加到Test.cpp:

namespace v
{
    int g = 9; // This is now the ONLY definition of 'g', in test.obj.
}