Is char *envp[] as a third argument to main() portable

In order to get an environment variable in a C program, one could use the following:

• getenv()
• extern char **environ;

But other than the above mentioned, is using char *envp[] as a third argument to main() to get the environment variables considered part of the standard?

#include <stdio.h>

int main(int argc, char *argv[], char *envp[])
{
    while(*envp)
        printf("%s\n",*envp++);
}

Is char *envp[] portable?

The function getenv is the only one specified by the C standard. The function putenv, and the extern environ are POSIX-specific.

###EDIT

The main parameter envp is not specified by POSIX but is widely supported.

> An alternative method of accessing the environment list is to declare > a third argument to the main() function: > > int main(int argc, char *argv[], char *envp[]) > > This argument can then be treated in the same way as environ, with the > difference that its scope is local to main(). Although this feature is > widely implemented on UNIX systems, its use should be avoided since, > in addition to the scope limitation, it is not specified in SUSv3.

It isn't portable. *envp[] is a traditional UNIX thing, and not all modern UNIX systems implement it.

Also as a side note you could access envp by doing a pointer traversal over *argv[], overflowing it...but i don't think that can be considered safe programming. If you take a look at the process memory map you will see that envp[] is just above argv[].

The Standard describes two formats for main (see 5.1.2.2.1 in the C99 Standard (pdf))

a) int main(void)

and

b) int main(int argc, char **argv) or equivalent

and it allows implementations to define other formats (which can allow a 3rd argument)

c) or in some other implementation-defined manner.

The 3rd argument is valid in Microsoft C and GNU GCC:

Visual Studio 2015: Arguments to main

GNU C Programming Tutorial: Environment variables