1	The C Preprocessor Yongjoon Lee April 22, 2005
2	What is it? Things with # #include <stdio.h> Processes the C source files BEFORE handing it to compiler. `Pre`-process gcc –E cpp
3	Why care? File Inclusion Basic Macros Parameterized Macros Conditional Compilation Style and (mis)use of Macros
4	File Inclusion Recall : #include <filename> #include <foo.h> System directories #include “foo.h” Current directories gcc -I
5	Macros We can #define constants #define HALF_PI 1.5708 #define BAD_PI HALF_PI+HALF_PI Solution? ((((((((((The parentheses!)))))))))) #define PI ((HALF_PI)+(HALF_PI))
6	Parameterized Macros Macros with param : #define BAAAD_DOUBLE(x) (x2) #define BAD_DOUBLE(x) ((x)+(x)) #define OKAY_DOUBLE(x) ((x)2) WHAT TO TAKE HOME: Don’t use 2+ parameters. No assignments within macro
7	Parameterized Macros cont’d Want to wrap malloc() calls. Can we? YES! #define NEW_T(t,sz) ((t) malloc((sz)sizeof(t))
8	Appropriate use of Macros Do Use parentheses Handle header file inclusion Capitalize macro names Don’t Use more than 2 parameters. Replace function calls with macros for ‘performance’ Make the code harder to read #define LOOP(s) while(1) {s};
9	Conditional Inclusion #if #ifdef #ifndef #elif #else #endif
10	Conditional Compilation Debugging #define DEBUG_MODE #ifdef DEBUG_MODE /* … Debug code … / #endif OS/Platform #ifdef _WIN32 #include <windows.h> #elif / …… */
11	File Header File header #ifndef FOO_H #define FOO_H /* … the whole file … * #endif Why??? Global variables Cycles of includes Inefficient
12	The Printf Yongjoon Lee April 22, 2005
13	Basics printf(“format string”,vars); Format string? “This year is %d\n” “Your score is %d\n” Conversion by % %d : int %f : float, double %c : char %s : char *, string %e : float, double in scientific form
14	Examples %d conversion Padding ( width ) %12d %012d Precision %12.4d %12.6d Left/right justification %12d %-12d Similar in %f, %e, … conversions
15	Example %c, %s conversion %c has only precision 1 Precision in %s means string length starting from the beginning Padding and justification are same