Preprocessor in C S-Teacher

1. INTRODUCTION TO C
PREPROCESSOR

2. C Preprocessor
Overview
Preprocessor Directives
Conditional Compilation

3. Overview
 Six phases to execute C:
1. Edit
2. Preprocess
3. Compile
4. Link
5. Load
6. Execute

4. C Preprocessor
All preprocessor directives begin with #
Possible actions
Inclusion of other files
Definition of symbolic constants & macros
Conditional compilation of program code
Conditional compilation of preprocessor directives

5. Preprocessor Directives
#define for symbolic constants
#define identifier text
 Creates symbolic constants
 The “identifier” is replaced by “text” in the program
Example
#define PI 3.14
area = PI * radius * radius;
 Replaced by “area = 3.14 * radius * radius” by
preprocessor before compilation

6. Conditional Compilation
Controls the execution of preprocessor directives
& compilation of code
Define NULL, if it hasn’t been defined yet
#if !defined(NULL)
#define NULL 0
#endif
Use to comment out code (for comments)
#if 0
code prevented from compiling
#endif

7. Conditional Compilation
Controls the execution of preprocessor directives
& compilation of code
Define NULL, if it hasn’t been defined yet
#if !defined(NULL)
#define NULL 0
#endif
Use to comment out code (for comments)
#if 0
code prevented from compiling
#endif