accessing environment variables

char * getenv(const char * name);

Alternately, environment variables may be accessed by using the special form of main():

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

At startup, the variable envp Is set to point to the process's environment, which is in the form of an array of C-strings. The last element in the array is a NULL pointer indicating the end of the array. This enables you traverse the entire array easily:

//execute loop so long as envp[n] isn't NULL
for (int n=0; envp[n]; n++) {
    cout << envp[n]<< endl;
}

setting environment variables

int putenv(const char * var);

var must be of the form varname=value. This does not affect the master environment, only the copy used by the currently running program, which is then inherited by any child processes.

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References:

http://www.informit.com/guides/content.aspx?g=cplusplus