understanding requirements for execve and setting environment vars

Question

We are having a lot of trouble interpreting our teacher. We asked for clarification and got the following back from him

1. For execve, send it a environment you se

Answer 1

I'm a little late to the party here, but if you want to preserve the old environment variables as well as creating your own, use setenv, and then pass environ to execve().

    setenv("dog", "spike", 1);
    extern char** environ;
    execve(argv[0], argv, environ);

environ is a variable declared in unistd.h, and it keeps track of the environment variables during this running process.

setenv() and putenv() modify environ, so when you pass it over execve(), the environment variables will be just as you'd expect.