Printing all environment variables in C / C++

Question

How do I get the list of all environment variables in C and/or C++?

I know that getenv can be used to read an environment variable, but how do I list th

Answer 1

int main(int argc, char* argv[], char* envp[]) {
   // loop through envp to get all environments as "NAME=val" until you hit NULL.
}

Answer 2

In most environments you can declare your main as:

main(int argc,char* argv[], char** envp)

envp contains all environment strings.

Answer 3

The environment variables are made available to main() as the envp argument - a null terminated array of strings:

int main(int argc, char **argv, char **envp)
{
  for (char **env = envp; *env != 0; env++)
  {
    char *thisEnv = *env;
    printf("%s\n", thisEnv);    
  }
  return 0;
}

Answer 4

int main(int argc, char **argv, char** env) {
   while (*env)
      printf("%s\n", *env++);
   return 0;
}

Answer 5

If you're running on a Windows operating system then you can also call GetEnvironmentStrings() which returns a block of null terminated strings.

Answer 6

Your compiler may provide non-standard extensions to the main function that provides additional environment variable information. The MS compiler and most flavours of Unix have this version of main:

int main (int argc, char **argv, char **envp)

where the third parameter is the environment variable information - use a debugger to see what the format is - probably a null terminated list of string pointers.