Printing all environment variables in C / C++

How do I get the list of all environment variables in C and/or C++?

I know that getenv can be used to read an environment variable, but how do I list them all?

The environment variables are made available to main() as the envp argument - a null terminated array of strings:

int main(int argc, char **argv, char **envp)
{
  for (char **env = envp; *env != 0; env++)
  {
    char *thisEnv = *env;
    printf("%s\n", thisEnv);    
  }
  return 0;
}

#include <stdio.h>

extern char **environ;

int main() {
  char **s = environ;

  for (; *s; s++) {
    printf("%s\n", *s);
  }

  return 0;
}

I think you should check environ. Use "man environ".

Your compiler may provide non-standard extensions to the main function that provides additional environment variable information. The MS compiler and most flavours of Unix have this version of main:

int main (int argc, char **argv, char **envp)

where the third parameter is the environment variable information - use a debugger to see what the format is - probably a null terminated list of string pointers.

LPTCH WINAPI GetEnvironmentStrings(void);

http://msdn.microsoft.com/en-us/library/ms683187%28VS.85%29.aspx

EDIT: only works on windows.

Printing all environment variables in C / C++

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