1 / 10

Preprocessor

Preprocessor. All preprocessor directives or commands begin with a #. E.g. #include <stdio.h> C program → Modified C program → Object Code Can appear anywhere in the program No “;” in the end. preprocessor. compiler. Preprocessor Directives. Macro definition #define, #undef

tpfister
Download Presentation

Preprocessor

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Preprocessor • All preprocessor directives or commands begin with a #. • E.g. #include <stdio.h> C program → Modified C program → Object Code • Can appear anywhere in the program • No “;” in the end preprocessor compiler

  2. Preprocessor Directives • Macro definition • #define, #undef • File inclusion • #include • Conditional Compilation • #if, #ifdef, #ifndef, #elseif, #else • Others

  3. #define • To define constants or any macro substitution.     #define <macro> <replacement name>   E.g.   #define FALSE 0 #define TRUE !FALSE • To undefined a macro. E.g. #undef FALSE #define D 2 printf("%d",D); #undef D int D=6; printf("%d",D);

  4. Define Functions • E.g. To get the maximum of two variables: #define max(A,B) A > B ? A:B • In the C code:    x = max(q+r,s+t);

  5. File inclusion • #include directive • Include the contents of another file at the point where the directive appears. • Why need file inclusion • Use built-in functions • E.g., printf(), rand(); • Reuse code double mean(int x,int y) { return (x+y)/2; } double mean(int ,int ); #include “test.h” printf("%f",mean(3,5)); test.cpp test.h Your code

  6. File inclusion formats • #include <file> • Used for system header files • File contain function prototypes for library functions • <stdlib.h> , <math.h> , etc • #include "file" • Used for header files of your own program • looks for a file in the current directory first • then system directories if not found

  7. Custom header files • Steps for creating custom header files • Create a file with function prototypes • Save as a .h file. E.g.: filename.h • Load in other files with • #include "filename.h" • Advantage • Reuse functions and data structure declaration

  8. Conditional compilation • Useful when • machine-dependencies • setting certain options at compile-time. • Expressions • #if expression • #ifdef expression (same as #if defined ) • #ifudef • #elif and #else • #endif

  9. Examples • Example: write programs that are portable to several machines or operating systems • #if defined(WINDOWS) • #elif defined(LINUX) • #elif defined(SOLARIS) • #endif • Example: Providing a default definition for a macro • #ifndef BUFFER_SIZE • #define BUFFER_SIZE 256 • #endif

  10. Inline functions Ret_Type inline func_name(params); e.g. int inline func(void); • Inline hints to the compiler that this function should be unrolled an inlined into wherever it is called. This can avoid function call overhead. • Problems with inline: • The compiler may happily ignore this. It’s kind of like the register keyword in this manner. It is merely a hint; it is not a command. • You may (and probably will) make your program size larger. • Read the previous bullet as “cache miss” or “page fault”.

More Related