The comma operator (,) works almost like the semicolon ;
that separates one C statement from another. You can separate almost
any kind of C statment from another with a comma operator. The
comma-separated expressions are evaluated from left to right and the
value of the whole comma-separated sequence is the value of the
rightmost expression in the sequence. Consider the following code
example.
#include <stdio.h>
/* To shorten example, not using argp */
int main (int argc, char *argv[], char *envp[])
{
int a, b, c, d;
a = (b = 2, c = 3, d = 4);
printf ("a=%d\nb=%d\nc=%d\nd=%d\n",
a, b, c, d);
return 0;
}
The value of (b = 2, c = 3, d = 4) is 4 because the value of its
rightmost sub-expression, d = 4, is 4. The value of a is
thus also 4. When run, this example prints out the following text:
a=4
b=2
c=3
d=4
The comma operator is very useful in for loops. (See The flexibility of for, for an example.)
