Thread: printf() bug? or..?

Compiler won't promote type for variadic function like printf.
Thus passing 1233423 means it's just integer for printf. You need to explicitly say the type (either cast or suffix will do for numbers).

E.g
printf("%f \n", 3 ); // won't work pass int. printf expects double.

You need to be consistent!!!!
Try

printf("=%lu =%lu\n", 11111111111UL, 11111111111UL);


Basic C program help
I think this kind of question is quite common.

Those constants are too big, even for unsigned long.

Try

Code:

$ gcc -Wall bar.c
$ ./a.out 
=11111111111 =11111111111
$ cat bar.c
#include<stdio.h>

int main ( ) {
  printf("=%llu =%llu\n", 11111111111ULL, 11111111111ULL);
  return 0;
}

Of course, you need a real C99 library to be able to deal with this properly.
If you're stuck with some fossil compiler, or are crippled by the MS runtime library that all the MinGW ports rely upon, you're pretty much stuck.

Originally Posted by juvan

Code:

printf("=%lu =%lu\n", 11111111111UL, 11111111111UL);

This does not work.

But this:

Code:

printf("=%llu =%llu\n", 11111111111ULL, 11111111111ULL);

works like a charm, even if I input something like:

Code:

printf("=%llu =%llu\n", 111111111111111111111111111111111111111111111ULL, 11111111111ULL);

The second number is correct, which is really my issue, I don't have the problem with printing BIG ARSE :P numbers, my problem was that the first number obviously somehow truncated the second one, and that was my real problem. But this works like a fairy tale.

BTW can anybody explain, why and how this works.

Thanks.

EDIT: I'm using Pelles C

It works because in PellesC unsigned long long is a 64 bit integer... thus ULL and %llu will accept values up to 64 bits...

Thus you have a range from 0 to 18,446,744,073,709,551,614

You can look all this up in your Pelles C help file ...
Open Poide click Help -> Contents ->C99 language reference->Declarations and types->Storage of basic types.

( A) Pelles C is probably the best documented compiler available B) why don't people ever look in help files on their own?)

It's probably a lot clearer to #include <stdint.h> and specify ... uint64_t ... for your variables.

However; your second one with that monster row of 1s should not work even there... If you have to do anything that produces numbers that big you should be working with one of the "bignum" libraries. (Google is your friend)

As I said, I don't care about printing large numbers and getting to see the right values, my problem was, when I at first said:

Code:

printf("=%lu =%lu\n", 11111111111, 11111111111); // Output: =2521176519 =2

And as you can see the second number got ruined because obviously the first one wrote over it. And that was my problem, but now with

Code:

%llu

it leaves the second number alone.

Well I may now enjoy some relaxation

Thanks for all your help guys.

EDIT: Since I am new here, is there any way to mark this thread as "SOLVED" ?

Originally Posted by juvan

And as you can see the second number got ruined because obviously the first one wrote over it. And that was my problem, but now with %llu it leaves the second number alone.

No, that's not what happened... you provided values that caused errors, the result is undefined. That means printf() displayed garbage. nothing was over-written or ruined. ... again READ THE HELP FILE... it's all there.

You are using a compiler that comes with a 1.2mb help file... do you think it might be helpful to actually read it?

Here's a little trick most people miss... put your text cursor on any keyword or library function call... Press F1... Oh my!

If you go to the Pelles C forums you can download a copy of the Windows SDK that will integrate into Pelles C and provide you documentation on basic Windows API calls with F1 as well...