what does "U" mean in a macro?

[tummala_005]

Hi,
Could some body tell me what exactly "U" means in a macro like,

#define INVALID  -1U

//Can I write in this way in C and also is it correct if I write some condition as follows in my code.

uint32 x;
----
---
if( x != INVALID )
{
-------
}

My intention is to check if X not equal to -1.

Thanks,
tummala

[matsp]

It's not to do with macro, but with "numbers", U means unsigned, so in this instance it says "A value of -1 that is unsigned". That helps when you want to assign an unsigned variable with the special value that is "all ones".

--
Mats

[tummala_005]

ok in that case will it serve the purpose in the code.
I was getting "integer conversion resulted in a change of sign" warning, if I don't put U.
But now I am not sure if placing U beside -1 makes it a 32 bit unsigned value??

[matsp]

The U makes it an unsigned value, yes. It doesn't say anything about the number of bits of the value. Hopefully uint32 is correctly defined, and thus will be a 32-bit value.

Basically, the U says "Look, this may look like a signed value, but I'd like you to treat it as it wasn't" to the compiler.

--
Mats

[tummala_005]

ok,that was helpful.
Thanks!!