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C Preprocessor

C Preprocessor. Overview Preprocessor Directives Conditional Compilation Predefined Symbolic Constants. Overview. Six phases to execute C: Edit Preprocess Compile Link Load Execute. C Preprocessor. All preprocessor directives begin with # Possible actions Inclusion of other files

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C Preprocessor

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  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 <filename> • 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 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

  8. Predefined Symbolic Constants #include <stdio.h> int main(){ printf("%d\n%s\n%s\n%s\n", __LINE__, __FILE__, __DATE__, __TIME__); } • Output: 3 example.c Oct 13 2003 19:27:57 • line #, file name, compiled date, compiled time • See example.c

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