Example of SetEnvironmentVariable and GetEnvironmentVariable

Sometimes you may want to communicate between different DLL's using some sort of flags. The simplest way to do it probably is using environment variable. Here is a simple example but can be modified to suit multiple DLL's.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include<iostream>
#include<atlstr.h>

using namespace std;

int main()
{
  //Suppose we want to have a temporary environment variable called "ZahidVar" whose value could be "120" or "140"
  string varName("ZahidVar");
  CString value;
  DWORD len = GetEnvironmentVariable(varName.c_str(), value.GetBuffer(100), 100);
  value.ReleaseBuffer();

  if(len)
    cout<<"Value of environment variable = "<<value<<endl;
  else
    cout<<"environment variable was empty"<<endl;

  //Set the environment variable now
  SetEnvironmentVariable("ZahidVar", "120");

  len = GetEnvironmentVariable(varName.c_str(), value.GetBuffer(100), 100);
  value.ReleaseBuffer();

  if(len)
    cout<<"Value of environment variable = "<<value<<endl;
  else
    cout<<"environment variable was empty"<<endl;

  return 0;
}

The output is as follows:


It should be noted that the scope of this environment variable is temporary and will cease to exist once the program exits.

You can also look at this example to show you how to print all the environment variables.