C doesn't have a bool? Also VS2010 question

Question

I\'m using VS 2010 Pro.

First, C doesn\'t have a bool type? I just have to use int with 0/1. Seems odd as most languages consider boolean a standard type.

Answer 1

See R.'s answer for information about the bool type.

Unfortunately, MSVC doesn't support C99 when it's compiling C code - it has bits and pieces (generally things in the C99 library that are required by C++), but for the most part it only supports C90.

As for bool still being highlighted in the editor - the highlighting in MSVC may be sophisticated, but it doesn't take into account the differentiation between C, C++, and C++/CLI. For example, if you use a construct that's CLI-only, it'll be highlighted as such even if your project has nothing to do with CLI.

Answer 2

C did not have an actual Boolean type until C99.

As a result, idiomatic C doesn't really use boolean-valued symbols or expressions as such (i.e., you won't see many explicit tests against "true" or "false"). Instead, any zero-valued integral expression or a NULL pointer will evaluate to "false", and any non-zero-valued integral expression or a non-NULL pointer will evaluate to "true". So you'll see a lot of code like:

foo *bar = malloc(sizeof *bar * ...);
if (bar) // equivalent to writing bar != NULL
{
   // bar is non-NULL
} 

Relational and equality expressions such as a == b or c < d will evaluate to an integral type with a value of either 1 (true) or 0 (false).

Some people introduce their own TRUE or FALSE symbolic constants by doing something like

#define TRUE  (1)  // or (!FALSE), or (1==1), or...
#define FALSE (0)  // or (!TRUE), or (1==0), or ...

Unforunately, some of those people occasionally manage to misspell 0 or 1 (or the expressions that are supposed to evaluate to 0 or 1); I once spent an afternoon chasing my tail because someone screwed up and dropped a header where TRUE == FALSE.

Not coincidentally, that was the day I stopped using symbolic constants for Boolean values altogether.

Answer 3

Concerning the bool type: In C, any non-zero value is regarded as "true" (and zero is "false"). This comes in handy when, say, checking the value of a pointer:

if ((ptr = malloc(sizeof(foo))) != 0) ...

can be shortened to:

if (ptr = malloc(sizeof(foo))) ...

C was designed to be a "mid-level" language, i.e. in-between assembler and traditional "high-level" languages. It was also designed to be compact/concise. So it has a minimalist flavor, exemplified in the its support for "shorthand" like the above, and also in the omission of a built-in Boolean data type (up to C99, as others have pointed out).

Many libraries/frameworks (ones that I'm aware of anyway) do something like the following

#define BOOL int
#define FALSE 0
#define TRUE (!FALSE)

This does mean that you should avoid directly comparing values/results to TRUE. Consider the following. Given int a = 2; int b = 3;, then both if (a) and if (b) evaluate to true, but a and b are not equal.

Concerning syntax highlighting: C++ does have a bool type, which I'm guessing is why the compiler highlights the word. However, the fact that your source file ends it .c marks it as C code, so the type isn't allowed. Seems like the syntax highlighting should catch this, though.

Concerning the absence of C components: If I understand the question correctly: the short answer is, in order to do "managed code" (ie .NET) development -- which is what you'd have to be doing in order to use .NET components -- you need to use a language supported by the .NET runtime, i.e. C#, VB(.NET), F#, or C++. (C++ is available in both "managed" and "unmanaged" flavors, meaning you can develop either against .NET or the Windows API.)

Are you under some sort of directive to use C as opposed to other languages?

Answer 4

Newest C standard (C99) has bool type indeed. Just include stdbool.h and you can use it. Unfortunately MSVC does not haver proper support for C at all. Only partial C89.

Answer 5

The current C language (C99) has a bool type (actually _Bool, but including stdbool.h declares a typedef alias bool for it), but since you're using MSVC, that's not available to you. In any case, using boolean types in C is completely non-idiomatic and largely useless. Just use int like everyone else. Or if you need a giant array of them, make your own bit-array implementation.

Answer 6

If you're developing in C, I'd recommend a different compiler as VC++ is not a modern C compilier and does not support the C99 standard. If you're on windows try MinGW, which basically gets you GCC with access to Windows-y API stuff.

If you're set on using Visual Studio, create your own header file to use instead of stdbool.h:

#pragma once

#define false   0
#define true    1

#define bool int

I found that Visual Studio 2010 complained if I tried to use a typedef instead of a #define to define bool.