printf("%8lx", int) is printing 16 characters

Question

My program includes the following code:

printf("%8lx", int);

And in kubuntu, when I run the program, it actually prints 16 chars, rather than 8. How is this possible?

it's considered a bad style to use a reserved word `int` as a variable name — lenik, Jul 28 '18 at 03:26
@KeineLust could we agree that it's not good and leave the exact wording of the compiler diagnostic to compilers? =) — lenik, Jul 28 '18 at 07:22
@lenik: well, it's not a matter of style ... `int string;` is bad style, but `int int;` is just wrong ;) — David Ranieri, Jul 28 '18 at 07:33
@lenik int is a reserved keyword. Surely you know what "reserved" means. — machine_1, Jul 28 '18 at 09:17
If you want to print the 8 low order hex digits, use `printf("%8lx", (unsigned long)(x & 0xFFFFFFFF));` — chqrlie, Jul 29 '18 at 15:32

score 3 · Accepted Answer · answered Jul 28 '18 at 03:19

3

That is correct, depending on the value of the integer. The width specifier is the minimum width, not the maximum width:

"Width: Minimum number of characters to be printed. If the value to be printed is shorter than this number, the result is padded with blank spaces. The value is not truncated even if the result is larger."

answered Jul 28 '18 at 03:19

EricS

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Oh thank you, then how do you limit the output to, say, 8 characters? – Uclydde Jul 28 '18 at 03:21
I think "%.8lx" will work. See this post: https://stackoverflow.com/questions/2239519/is-there-a-way-to-specify-how-many-characters-of-a-string-to-print-out-using-pri – EricS Jul 28 '18 at 03:29
1

"how do you limit the output to, say, 8 characters?" --> Research `snprintf()`. – chux - Reinstate Monica Jul 28 '18 at 03:34
1

If you limit the output to 8 characters, you will lose data. Are you sure that's what you want? – Steve Summit Jul 28 '18 at 09:52

autistic · Answer 2 · 2018-07-29T15:11:53.650

it's considered a bad style to use a reserved word int as a variable name – lenik 31 mins ago

It's not just bad style; it's a constraint violation. There's no way this code could compile, let alone produce the symptoms you describe. That aside, if we take time to reconstruct some semblance of an MCVE, and try to compile it, well, first the MCVE...

#include <stdio.h>
int main(void) {
    printf("%8lx\n", (int){42});
}

My compiler is warning me... did you see that warning there? In fact, ideone.com flat out refuses to compile and run even this more complete code... It's complaining about format ‘%lx’ expects argument of type ‘long unsigned int’, but argument 2 has type ‘int’... That makes sense, because %lx tells printf to expect a long unsigned int argument, but we've passed printf an int instead...

I'd like to attribute to this answer the book K&R2E, for those who are trying to learn without one, as I am legally entitled to do so according to section 4C. b. i. of the Creative Commons Legal Code which governs StackOverflows content license. No matter how unpopular this message may be, it is dangerous to learn C without a book.

printf("%8lx", int) is printing 16 characters

2 Answers2