How to list all environment variables in a c / C ++ application

Question

I know that when programming in C ++ I can access individual environment variables using getenv .

I also know that in the os x terminal I can display ALL current environment variables using env .

I'm interested in getting a complete list of environment variables available for my current C ++ program. Is there a c / C ++ function that will list them? In other words, is there a way to call env from my C ++ code?

Answer 1

Use the global environ variable. This is a null-end pointer for an array of strings in the format name=value . Here's a miniature clone of env :

 #include <stdlib.h> #include <stdio.h> extern char **environ; int main(int argc, char **argv) { for(char **current = environ; *current; current++) { puts(*current); } return EXIT_SUCCESS; } 

Answer 2

You can use the envp argument for main :

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

and as a bonus, apparently on OSX you have apple , which gives you other information provided by the OS:

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

But what is it used for? Well, Apple can use the apple vector to pass any “hidden” parameters that they want for any program. And they really use it. Currently apple [0] contains the path where the executable binary was found on disk. What are you saying? How is apple [0] different from argv [0]? The difference is that argv [0] can be set to any arbitrary value when execve (2) is called. For example, shells often distinguish an input shell from a regular shell by launching an input shell with the first character in argv [0], which is a -

Answer 3

Oops, I forgot that system allows you to execute terminal commands.

This snippet gives me what I need:

 std::cout << "List of environment variables: << std::endl; system("env");