using #define

Jo_Nak · 06-10-2003, 02:07 PM

Hi,

this is a simple question, but to which I couldn't find an answer. In a header file, if '#define' is used this way for example:

struct video
{
int ...;
cahr...;

#define VCTX 1

int...;
}

Is VCTX gonna be available in .c file as a global variable or it can only be used inside this structure?

Thanx

kev82 · 06-10-2003, 02:59 PM

# directives such as define are processed before the code reaches the compiler. VCTX can be used anyehere after its been #defined. it seems quite odd to find it in the middle of a structure definition though.

coolman0stress · 06-10-2003, 05:17 PM

yes #define is a preprocessor directive, just before compiling the preprocessor scans your files and replaces any VCTX with the value 1. It's just one form of a macro (often also called a symbol constant definition).

croakofonix · 06-11-2003, 01:37 PM

#define is a preprocessor statement. Also the golden rule in C is "Define Before Usage". So i think that the replacement will only be done for the lines that occur after the #define directive.

coolman0stress · 06-11-2003, 01:46 PM

Yes that's why you usually find #defines at the very top, otherwise the compiler will bitch if it finds something not previously defined.