In C Language, the "#ifdef" directive is a preprocessor directive used for conditional compilation. #ifdef stands for "if defined" and is used for conditional compilation.
It checks whether a specific macro has been defined using the #define directive.
If the macro has been defined, the code block between `#ifdef` and `#endif` is included in the compilation process. Otherwise, it is skipped.
#ifdef macro_name
// Code to be compiled if macro_name is defined
#endif
If "macro_name" is defined using "#define".
The code between "#ifdef" and "#endif" will be included in the compilation. Otherwise, it will be ignored.
#include <stdio.h>
#define DEBUG_MODE
int main() {
#ifdef DEBUG_MODE
printf("Debug mode is enabled.\n");
#else
printf("Debug mode is disabled.\n");
#endif
printf("Normal execution.\n");
return 0;
}
Debug mode is enabled. Normal execution.
"DEBUG_MODE" is defined using #define.
The "#ifdef" DEBUG_MODE directive checks whether "DEBUG_MODE" is defined.
Since it is defined, the code within the "#ifdef" and "#else" blocks will include the debug mode message during compilation.
If "DEBUG_MODE" were not "defined", only "Normal execution." would be printed.
#include <stdio.h>
#define USE_FEATURE_X
int main() {
#ifdef USE_FEATURE_X
printf("Feature X is enabled.\n");
#else
printf("Feature X is disabled.\n");
#endif
return 0;
}
Feature X is enabled.
"USE_FEATURE_X" is defined using "#define".
By toggling the definition of "USE_FEATURE_X", we can enable or disable feature "X" in your program.
The "#ifdef USE_FEATURE_X" directive checks whether feature "X" is enabled, and the corresponding message is printed during compilation.
How "#ifdef" can be used for conditional compilation in C programming.
Allowing us to include or exclude specific code based on the presence or absence of defined macros.
It's a powerful feature for managing different build configurations and platform-specific code in your programs.