Uses of C comma operator [duplicate]

Question

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• What does the comma operator , do? 8 answers

You see it used in for loop statements, but it's legal syntax anywhere. What uses have you found for it elsewhere, if any?

Answer 1

Two killer comma operator features in C++:

a) Read from stream until specific string is encountered (helps to keep the code DRY):

 while (cin >> str, str != "STOP") {
   //process str
 }

b) Write complex code in constructor initializers:

class X : public A {
  X() : A( (global_function(), global_result) ) {};
};

Answer 2

The Boost Assignment library is a good example of overloading the comma operator in a useful, readable way. For example:

using namespace boost::assign;

vector<int> v; 
v += 1,2,3,4,5,6,7,8,9;