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GCC for 64 bit Platform

When you are using 64 bit version of Linux OS, All the software are by default work in 64 bIt Mode.
In the 64 bit Mode the Integral(integer) part only extended but floating point numbers remains constant more info .
For Ex:
long datatype holds 8 byte. The Data size is defined by Application Binary Interface (ABI),More info http://www.x86-64.org/documentation/abi.pdf

Sample C program:

#include <stdio.h>
int main(){
 long vLongVar=1;
 
 if(sizeof(vLongVar)==8){
      printf("This is 64 bit Platform");
 }else if( sizeof(vLongVar)==4){
      printf("This is 32 bit Platform");
 }
 
}