I'm trying to write my own version of getenv. I haven't started yet so I'm trying to understand environ first.
If it's a global why can't I print it in my function? Is environ a String or an array of chars? Why is environ a double pointer? Thank you.
#include <iostream>
#include <string>
#include <stdlib.h>
void myenv(char*);
void myenv(char* name)
{
std::cout<<environ;
}
int main(int argc, char** argv, char** environ)
{
myenv("PATH");
}
environ is a char**. It points at an array of char*, each of which points to a string of char. So it's like an array of strings. For example, environ[0] is a null-terminated string. Try printing out that:
std::cout << environ[0];
Each string is an environment variable of the form name=value. They correspond to the environment variables for the current process.
However, environ is not a feature of C++ and is non-portable. It comes from the unistd.h header which is defined by POSIX.
Its a char ** containing the env. variables
extern char **environ;
http://pubs.opengroup.org/onlinepubs/007908799/xsh/environ.html
Just adding;
Is environ a String or an array of chars? Why is environ a double pointer?
environ addresses an array of pointers, that each point to the first address of a character string. The environment isn't one string, it is a bunch of strings (well, the environment could be empty, so that "bunch" can be zero).
environ[0] contains a pointer to the 'first' environment variable.
environ[1] contains a pointer to the 'second'.
environ[0][0] would reference the first character of the 'first' name in the environment.
environ[1][0] would reference the first character of the 'second' name.
Or if there isn't at least two environment variables, environ[1] points off into segfault land or worse, random memory.
I quoted first and second, as there are no defined rules as to how environment name strings are ordered, (don't expect the names to be alphabetical order for instance).
