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•
Description
The #define directive defines string constants that are substituted into
a source line before the source line is evaluated. The main purpose is to
improve source code readability and maintainability. If the replaced-text
requires more than one line, the backslash (\) is used to indicate multiple
lines.
•
Example
#define TOTAL_COUNT 40
#define USERNAME "Henry"
#define MAX(a,b) ((a>b)?a:b)
→
#error
•
Syntax
#error
" message-string"
•
Description
The #error directive generates a user-defined diagnostic message, mes-
sage-string.
•
Example
#if TOTAL_COUNT > 100
#error "Too many count."
#endif
→
Conditional inclusion: #if #else #endif
•
Syntax
#if
expression
source codes
[
#else
source codes]
#endif
•
Description
The #if and #endif directives pairs are used for conditionally compiling
code depending upon the evaluation of the expression. The #else which
is optional provides an alternative compilation method. If the expression
is nonzero, then the source code below the #if statement will be compiled.
Otherwise, the source code that follows the #else statement, if it exists,
will be compiled.
•
Example
#define MODE 2
#if MODE > 0
#define DISP_MODE MODE
#else
#define DISP_MODE 7
#endif
Chapter 9 Holtek C Language
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