What is a comma separated set of assignments?

I noticed in a routine

  *pbuf++ = '%', *pbuf++ = to_hex(*pstr >> 4), *pbuf++ = to_hex(*pstr & 15);

Why does it work?

What does it do?


A comma operator is a sequence point : each comma separated expression are evaluated from left to right. The result has the type and value of the right operand. Functionally, your example is equivalent to (the much more readable ?) :

    *pbuf++ = '%';
    *pbuf++ = to_hex(*pstr >> 4);
    *pbuf++ = to_hex(*pstr & 15);

Here is another example that the standard provides for the comma operator (6.5.17) :

In the function call

f(a, (t=3, t+2), c)

the function has three arguments, the second of which has the value 5.

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