C Preprocessor

1
C Preprocessor

• Overview
• Preprocessor Directives
• Conditional Compilation
• Predefined Symbolic Constants

2
Overview

• Six phases to execute C
• Edit
• Preprocess
• Compile
• Link
• Load
• Execute

3
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

4
Preprocessor Directives

• include preprocessor directive
• include ltfilenamegt
• For standard library header files
• Location based on system
• include "filename"
• For programmer-defined header files
• Function, structure, typedef definitions global
  variables
• Located in the same folder as the file being
  compiled

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
Preprocessor Directives

• define for macros
• define macro-identifier text
• Can have arguments
• The macro is expanded in the program
• Example
• define AREA(x) ( (PI) (x) (x))
• circle_area AREA(5)
• Expanded to circle_area ((3.14)(5)(5)) by
  preprocessor before compilation

7
Conditional Compilation

• Controls the execution of preprocessor directives
  compilation of code
• Define NULL, if it hasnt been defined yet
• if !defined(NULL)
• define NULL 0
• endif
• Use to comment out code (for comments)
• if 0
• code prevented from compiling
• endif

8
Predefined Symbolic Constants

• include ltstdio.hgt
• int main()
• printf("d\ns\ns\ns\n", __LINE__,
  __FILE__, __DATE__, __TIME__)
• Output
• 3
• example.c
• Oct 13 2003
• 192757
• line , file name, compiled date, compiled time
• See example.c