comma operator in C

ta0kira · 04-25-2008, 09:27 AM

The orders of precedence of , and && are completely different. Comma is appropriate in some cases:

Code:

#include <stdio.h>

int main()
{
	int one, two;

	one = 1, two = 0;

	fprintf(stderr, ", : %i %i\n", one, two);

	one = 1 && (two = 0);

	fprintf(stderr, "&&: %i %i\n", one, two);

	return 0;
}

ta0kira

ta0kira · 04-25-2008, 09:57 AM

The operands of , are all evaluated, also, even if one or more are false:

Code:

#include <stdio.h>

int main()
{
	int I, J, K;

	I = J = 1;
	K = (I = 0) && (J = 0);

	fprintf(stderr, "1: %i %i %i\n", I, J, K);

	I = J = 1;
	K = (I = 0, J = 0);

	fprintf(stderr, "2: %i %i %i\n", I, J, K);

	I = J = 1;
	for (I = 0, J = 0; I || J; J = 0, I = 0)
	fprintf(stderr, "3: %i %i\n", I, J);

	I = J = 1;
	for ((I = 0) && (J = 0); I || J; (J = 0) && (I = 0))
	fprintf(stderr, "4: %i %i\n", I, J);

	fprintf(stderr, "5: %i %i\n", I, J);

	return 0;
}

ta0kira