Author: Bo Persson
Date: 04:59:42 09/26/03
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On September 26, 2003 at 06:50:59, Gerd Isenberg wrote: >Hi All, > >in C++ we have the boolean type "bool" with the value range true/false. >I'm not sure about ANSI-C. There is a _Bool type in C99. If you include bool.h you get the usual typedefs etc for bool, true, and false. > >Due to some C-related "portability" problems and possible performance drawbacks >due sizeof(bool) == 1 implies partial register handling or zero extending to >native word lenght, you find in most MS-sources an "own" boolean type BOOL: > >typedef int BOOL; // e.g. WINDEF.H The reason for this is not performance, but that Windows is older than standard C and C++. There was no bool type back then. You don't really have to extend the value to test for zero/non-zero. If you have several bools in a struct, the smaller size could be good too. > >This own BOOL type is of course not "typesafe" as bool, as you may assign any >"int" expressions to it. With BOOL one should interprete zero as FALSE and any >other value as TRUE. Due to this ambiguity, comparing BOOL-expressions with TRUE >may be erroneous, so better compare with != FALSE. There are also potential overload problems. > >See also this bugreport related to this issue: > >http://www.codeproject.com/buglist/virtualboolbug.asp > >Actually i have some "disputes" with colleagues obout it. >I found bool better for didactical reasons, >but stay with BOOL for pragmatical reasons. > >A few questions: > >Is sizeof(bool) == 1 per definition, >or is it compiler implementation depending? That is up to the compiler. > >Is there any conditional preprocessor directive to ask whether a user defined >type is already typedefined, similar to #ifdef? No. > >What is your opinion / experience with bool versus BOOL? I use bool as much as possible. BOOL is just for interfacing with Windows. > >Thanks in advance for your suggestions, >Gerd Bo Persson
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