c - for loop missing initialization

Question

I've seen

for(;;)

and

for ( ; *s != ''; s++)

Why is it blank like that. Thanks.

Answer 1

The for statement works like:

for (initialization; test-condition; update)

And any or all of those three can be omitted (left blank). So:

• for (;;) is an infinite loop¹ equivalent to while (true) because there is no test condition. In fact, for (int i=0; ;i++) would also be an infinite loop¹.

• for ( ; *s != ''; s++) is a loop with no initialization. s will point to the beginning of (probably) a string and is incremented until it reaches the null character '' denoting end-of-string. This essentially means loop through all characters of the string s

¹ The loop will still be interrupted if there's a break statement in the loop body, or a call to exit(), etc...