Simple way to manage global variables in c or cpp

2 comments on "Simple way to manage global variables in c or cpp"

• mgarcia: 2019-01-14 13:49 +1100
  A quick post...
  
  Yes I use globals where necessary, and no, I'm not ashamed to admit it!
  
  So this is how I handle global definitions and their instantiation.
  
  I have many header files where I define global variables, they are prefixed with INSTANCE.
  Before that I have a simple #ifdef checking if a precompiler define exist, INSTANCE_VARS_HERE.
  
  // global variables defined in a header file like this
  #ifdef INSTANCE_VARS_HERE
  #define INSTANCE
  #else
  #define INSTANCE extern
  #endif
  
  INSTANCE int g_counter;
  
  
  
  If the header files are used normally in a .cpp file it will reference all the global variables as external, which is normal.
  
  But in my globals.cpp file, where I want all my global variables instantiated, I tell the header file to instantiate the variables here by defining the INSTANCE_VARS_HERE prior to including the header.
  
  
  // in the c/cpp file where to instance the vars
  #define INSTANCE_VARS_HERE
  #include "include_file1.h"
  #include "include_file2.h"
  
  This will instantiate all the global variables into a single compiled file, which can be helpful keeping track of heap space and reading the NMAP file.

• mgarcia: 2019-03-03 12:48 +1100
  Adding to above, I came across this:
  
  #pragma once
  
  #ifdef __MAIN__
  #define __EXTERN(type, name, value) type name = value
  #else
  #define __EXTERN(type, name, value) extern type name;
  #endif
  
  and then declare your variables in that same header file, like such:
  
  __EXTERN(volatile int, MyVolatileInteger, 0);
  
  
  Which is pretty cool also, posted here:
  https://stackoverflow.com/questions/2544852/using-the-same-variable-across-multiple-files-in-c