Question

Please complete the following code in C using the comments as instructions. Further instructions are below the code.

challenge.c

// goal: print the environment variables to the file "env.txt", one per line

// (If envp is NULL, the file should be empty, opening in write mode will do that.)

// example:

// inputs:

// envp/environ = {"E1=2","E2=7",NULL}

// outputs:

// env.txt as a string would be "E1=2\nE2=7\n"

// example:

// inputs:

// envp/environ = {NULL} or NULL

// outputs:

// env.txt as a string would be ""

//

// TODO: write and complete the main function

int main()

{

return 0;

}

---

INSTRUCTIONS.txt

You are given a file, challenge.c.

You may edit this file as you wish.

All the work you need to do is in challenge.c.

You are making an entire program in challenge.c (so a main function needs to be in there)

All this program does is print the environment variables to a file called "env.txt"

Each variable is followed by a newline character

example:

inputs:

envp/environ = {"E1=2","E2=7",NULL}

outputs:

env.txt as a string would be "E1=2\nE2=7\n"

example:

inputs:

envp/environ = {NULL} or NULL

outputs:

env.txt as a string would be ""

Answer 1

#include <stdio.h> 
extern char **environ;
int main(void) 
{ 
        int i; 
        FILE * fp;
        fp = fopen ("env.txt","w");
        for (i = 0; environ[i] != NULL; i++){
            if(environ[i]==NULL){
                fp = fopen ("env.txt","w");
                fprintf (fp, "");
            }
            fprintf (fp, "%s\n",environ[i]);
        }
        fclose (fp);
        return 0; 
} 

you can also get at the environment via environ, even in functions other than main(). The variable environ is unique amongst the global variables defined by POSIX ans is not declared in any header file, so you must write the declaration yourself.

extern char **environ means the list of environments.