Use .ini methods, supported by Windows API to set environment variables for C++ applications. -To Read

GetPrivateProfileString(
  __in   LPCTSTR lpAppName,
  __in   LPCTSTR lpKeyName,
  __in   LPCTSTR lpDefault,
  __out  LPTSTR lpReturnedString,
  __in   DWORD nSize,
  __in   LPCTSTR lpFileName
);

-To Write

WritePrivateProfileString(
  __in  LPCTSTR lpAppName,
  __in  LPCTSTR lpKeyName,
  __in  LPCTSTR lpString,
  __in  LPCTSTR lpFileName
);

ex) init.ini

-------------------------
[INPUT_VAL]
val1 = Test1
val2 = Test2
--------------------

To load .ini parameters,

char
Temp[100];
GetPrivateProfileString("INPUT_VAL","val1","NOT_FOUND",Temp,100,"./init.ini");

To Write .ini parameters,

WritePrivateProfileString(("INPUT_VAL","val1","Test10","./init.ini");