C++ long long issues

Question

I've been using signed long longs and have had weird issues with it - i.e. inconsistent behavior. I.e.

long long i;
printf("%d", i);

This tends to print values which have no relevance to the actual value of i (this also occured with cout).

It also has random behavior with %, i.e.

if(i % x == 0)
        //some code

This would sometimes run i.e. if i = 15 and x = 5 it just wouldn't return true and therefore the if statement would not run the code.

It would tend to return true on x = 7 for some reason.

I believe that it may be a fault with the compiler which I believe was just the g++ compiler (it was at a competition).

Any ways to mitigate this or why it was doing this would be greatly appreciated.

`long long i; printf("%d", i);` This is **Undefined Behavior**. — cpplearner, Feb 21 '16 at 09:45
@Cjen1 _"I believe that it may be a fault with the compiler ..."_ That's a very rare case, most of the time it's your code that has the bug. — πάντα ῥεῖ, Feb 21 '16 at 09:47
Perhaps reading http://linux.die.net/man/3/printf might help — Ed Heal, Feb 21 '16 at 09:48
In C++ you should use `cout` instead and ignore the type specifier problem http://stackoverflow.com/q/6400180/995714 http://stackoverflow.com/q/2844/995714 — phuclv, Feb 21 '16 at 09:56
With your mod problem, what happended when you assigned the result of 'i % x' to a temp var and printed it out? — Martin James, Feb 21 '16 at 10:17
@Cjen1 _"I got the incorrect answer (that was with cout)"_ Can you provide a [MCVE] please? — πάντα ῥεῖ, Feb 21 '16 at 11:03

score 0 · Answer 1 · answered Feb 21 '16 at 10:56

0

To print the various integer types using printf-style syntax requires horrible syntax - I suggest using the C++ type-safe iostreams instead.

answered Feb 21 '16 at 10:56

Erik Alapää

1 Answers1