Obscure C++ syntax [duplicate]

This question already has answers here: Closed 12 years ago.

Possible Du开发者_运维知识库plicate:

C++ Comma Operator

About a year ago I noted some obscure syntax in a coding project I was working on:

table_value = table_index += 2, valueFromTable(table_index);

Does anyone recognise this?, it's like an assignment with an additional statement. This compiled in our entire suite of cross-platform compilers, so I'm pretty certain its valid C++ but I've never seen anything like it.

Any insight would be appreciated.

Gearoid

EDIT: heres some working code:

#include <iostream>
using namespace std ;

int valueFromTable(int a) { return a ; }

int main()
{
  int table_index = 0 ;
  int table_value = table_index += 2, valueFromTable(12);
  cout<<table_value<<endl;
  return 0 ;
}

---

This is the Comma operator.
It's standard C and C++ but heavily frowned upon.

It evaluates both arguments, and returns the result of the second.