How to check if a constant is suitable at compile time?

Question

I would like to add compile time to the following C ++ code (compiled with Visual C ++ 9):

//assumes typedef unsigned char BYTE;
int value = ...;
// Does it fit into BYTE?
if( 0 <= value && value <= UCHAR_MAX ) {
    BYTE asByte = static_cast<BYTE>( value );
    //proceed with byte
} else {
    //proceed with greater values
}

The problem is UCHAR_MAXboth BYTEindependent typedef, and when this code is ported, it can happen that they come out of sync and the code breaks. So I wanted to do something like this:

compileTimeAssert( sizeof( BYTE ) == sizeof( UCHAR_MAX ) );

but VC ++ 9 creates a "negative index" error when compiling that - it sizeof( UCHAR_MAX )has a value of 4, not 1.

How can I do the compile time check that I want?

Answer 1

You can check at compile time that ( (1 << (sizeof(BYTE)*CHAR_BIT)) - 1 ) == UCHAR_MAX.

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Answer 2

'' std:: numeric_limits <BYTE> :: max() UCHAR_MAX

Answer 3

BOOST_STATIC_ASSERT.

Answer 4

V++ 9 " " - sizeof (UCHAR_MAX) 4, 1.

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#define MAX 255;

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Answer 5

UCHAR_MAX - unsigned char. unsigned char 1 . , BYTE 0.. UCHAR_MAX -(UCHAR_MAX/2+1).. UCHAR_MAX/2, , sizeof(BYTE) == 1

, - int BYTE, :

if (!(value & ~(BYTE)-1)) ...