c++namespacesg++

How to refer to the pointer **environ in a user-defined namespace's member function?

#include <iostream>

namespace A {
    void func();
}

void  A::func()
{
    extern char **environ;
    std::cout << environ[0] << std::endl;
}

int main()
{
     A::func();
     return 0;
}

Like the code above, I just want to use the system-defined pointer **environ in A::func(), but g++ always says: 

undefined reference to `A::environ'

How can I use the system-defined variable environ correctly?

Solution

  • Add

     #include <unistd.h>

    and environ must be in global scope.

    So the code would look like this:

    #include <iostream>
#include <unistd.h>
extern char **environ;
namespace A {
void func();
}

void  A::func()
{

    std::cout << environ[0] << std::endl;
}

int main()
{
     A::func();
     return 0;
}