where is the definition of extern char **environ?

Question

we can get the environment variable in C like this:

extern char **environ;
int main(int argc, char *argv[])
{
    int count = 0;

    printf("\n");
    while(environ[count] != NULL)
   {
         printf("[%s] :: ", environ[count]);
         count++;
   }

   return 0;
}

but where is the defination of environ? I can't find that in unistd.h. and how does it work?

Answer 1

environ is defined as a global variable in the Glibc source file posix/environ.c.