List environment variables with C in UNIX

Question

Is there a way to enumerate environment variables and retrieve values using C?

Answer 1

Take a look at the environ global variable.

extern char **environ;

It might be defined in unistd.h (take a look at the environ (5) man page above).

Here's a little code demo I wrote:

#include <stdio.h>
extern char **environ;

int main()
{
    for (char **env = environ; *env; ++env)
        printf("%s\n", *env);
}

Here's how to use it:

matt@stanley:~/Desktop$ make enumenv CFLAGS=-std=c99
cc -std=c99    enumenv.c   -o enumenv
matt@stanley:~/Desktop$ ./enumenv 
ORBIT_SOCKETDIR=/tmp/orbit-matt
SSH_AGENT_PID=1474
TERM=xterm
SHELL=/bin/bash
... (so forth)