Sequence points in C / function calls

Question

I'm just learning some C, or rather, getting a sense of some of the arcane details. And I was using VTC advanced C programming in which I found that the sequence points are :

• Semicolon
• Comma
• Logical OR / AND
• Ternary operator
• Function calls (Any expression used as an argument to a function call is finalized the call is made)

are all these correct ?. Regarding the last one I tried:

void foo (int bar) { printf("I received %d\n", bar); }

int main(void) 
{

  int i = 0;

  foo(i++);

  return 0;

}

And it didnt print 1, which according to what the VTC's guy said and if I undertood correctly, it should, right ?. Also, are these parens in the function call the same as the grouping parens ? (I mean, their precedence). Maybe it is because parens have higher precedence than ++ but I've also tried foo((i++)); and got the same result. Only doing foo(i = i + 1); yielded 1.

Thank you in advance. Please consider that I'm from South America so if I wasnt clear or nothing makes sense please, oh please, tell me.

Warmest regards, Sebastian.

Answer 1

Your code is working like it should and it has nothing to do with sequence points. The point is that the postfix ++ operator returns the non-incremented value (but increments the variable by 1 nonetheless).

Basically:

• i++ – Increment i by one and return the previous value
• ++i – Increment i by one and return the value after the increment

The position of the operator gives a slight hint for its semantics.