Preprocessor examples

Conditional compilation

#define DEBUG_1 0

//Because DEBUG_1 is set to zero, the else 
//clause will be removed from code before compilation.
#if DEBUG_1 == 0
    processNoDebug();
#else
    processWithDebug()
#endif

#ifdef VERBOSE
    printVerboseLog();
#endif

Diagnostics directives

#define SYS_MODE 16

#ifndef SYS_OS
    #error "OS variable must be set."
#endif

#define RUN_MODE 32


#if SYS_MODE != RUN_MODE
    #warning "System does not match target architecture. May cause compilation errors."
#endif

#pragma message "User msg"

Macro operators

#define VAR_NAME(NUM) var##NUM
#define STRINGIFY(ARG) #ARG

int VAR_NAME(1) = 8; // int var1 = 8;
int VAR_NAME(2) = 16; // int var2 = 16;

printf("%s\n", STRINGIFY(x==0));

Macros

#define A 123
#define B 42

#define min(X, Y)  ((X) < (Y) ? (X) : (Y))

#define SWAP(a, b) {          \
                      a ^= b; \
                      b ^= a; \ 
                      a ^= b; \
                   } 



"Example A:" A
"Example B:" B
"min: "  min(A,B)
"swap: " SWAP(4,5)

Simple include

#include <stdio.h>

Special macros

__FILE__
__DATE__
__TIME__
__GNUC__
__LINE__
__GNUC_MINOR__