Incrementing pointers in for loop in C

[caryaharper]

I’ve been wanting to take a look at a lower level language and C seemed like a good pick, and I’ve been messing around with trying to iterate through a string with the use of a pointer and print each character, but the pointer seems to be going up by 4 each time and I don’t know why.

#include <stdio.h>

int main() {
	char name[4] = "Name";
	int *i;
	for (i = &name[0]; *i != "\0"; i++) {
		printf("i: %x\n", i);
		printf("%c\n", *i);
	}
	
	return 0;
}

The output looks something like:

Runtime error #stdin #stdout 0s 5416KB
i: 58fe6ef4
N
i: 58fe6ef8

i: 58fe6efc

i: 58fe6f00

It may be an infinite loop as the terminating condition is never met, but I’m using a playground so I don’t do anything too bad.

[JeremyLT]

This is not a great way to iterate through a string, FWIW.

You declared i as an int pointer, so it’s value is increasing by the size of an int. The standard int is 32 bits, or 4 bytes. You would need to declare i as a char pointer to get the behavior you expect.

But as a general rule, I strongly recommend against incrementing pointers. You get much clearer symantics by using an index variable.

[caryaharper]

That was the issue. I do understand the dangers of using a pointers in the loop because if you did it wrong like I did you end up pointing to unexpected places in memory. I was curious of pointer manipulation and getting the data from the memory location, and this seemed like an easy way to see it in action.

A lot more stuff to be careful of than JavaScript, but once I can say “Hello World” in all programming languages my resume will be flawless.

[JeremyLT]

It’s worth understanding how pointer incrementing works. I just like reminding people that it isn’t something that goes in production code.

Understanding pass by value vs pass by reference gets much easier once you understand pointers in C.

@caryaharper

once I can say “Hello World” in all programming languages my resume will be flawless.

Given the thousands of programming languages out there… I wouldn’t shoot for this as a goal, personally.