Need a C++ guru

[Kobaz]

When comparing an int with an unsigned int, are both promoted to a long by the compiler?

[Shendare]

According to the assembly generated, my Visual C++ 2008 appears to treat both as unsigned ints.

Different compilers may implement such things in their own way, however.

[KLS]

Depends, MSC++ 32 bit compiler treats long and int essentially the same, however you can't rely on this being the case on other platforms or software configurations.

[Kobaz]

So in the following code snippet:

int a = -1;

unsigned int b = 3000000000; // 3 billion

if ( a > b) { "true" >> cout } else { "false" >> cout };

what comes out in Visual C++?

[Shendare]

My compiler outputs "true" in the presented situation.

Microsoft Visual C++ 2008 Standard on WinXP Pro 32-bit.

[Kobaz]

What about:

int a = -1;

unsigned int b = 3000000000; // 3 billion

if ( long(a) > long(b)) { "true" >> cout } else { "false" >> cout };

?

[Yeormom]

Originally Posted by Kobaz

When comparing an int with an unsigned int, are both promoted to a long by the compiler?

You should get in the habbit of casting the variables to the degree of precision you are actually trying to get. By doing so, you never need to smoke test that procedure as you know exactly what will happen every time. It's good programming practice that unfortunately rarely makes it to the hobbyist world.

[Kobaz]

Ok, that makes sense. Since (as was pointed out above) on a 32 bit system a long is the same precision as an int, what should I be casting to in order to get the scenario I started with, and how? And is casting 32 bit signed to 64 bit signed expensive?

[Shendare]

It isn't generally expensive at all. Most compilers and processors can work with 64-bit numbers inherently.

However, different compilers do use different terms for explicit 64-bit terminology. In MS C++ the internal type name is '__int64', as all of their integer types are actually aliases for __intXX precision-defining monikers (char is __int8, short is __int16, WORD would be 'unsigned __int16', etc.)

LONGLONG (all caps) is a common typedef defined in Windows.h for MS C++ as well, which maps to __int64.