Re: bool implementation

From: Doug Harrison [MVP] (dsh_at_mvps.org)
Date: 01/15/05 

Date: Sat, 15 Jan 2005 07:00:14 -0600

Mark Randall wrote:

>Might as well use char or unsigned char, both evaluate likewise to true,

There are big differences between those types and bool. Conversion from
non-bool to bool essentially goes like this:

 // x is bool, y is non-bool integral type or pointer
 x = y != 0; // What you really get when you say x = y;

Besides working for pointers, bool does the right thing for wider types. For
example:

unsigned x = 0x100;
unsigned char y = x;
bool z = x;

Now, x is considered "true" for all values != 0. Assuming VC's data types, y
is false for all values of x >= 0x100. However, z is true whenever x is
"true".

>small performance hit tho.

Using a bool can indeed result in a small performance hit when assigning
values of types other than bool to it, due to the conversion performed. 

-- 
Doug Harrison
Microsoft MVP - Visual C++

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