The #ifdef identifier statement is equivalent to #if 1 when identifier has been defined. It’s equivalent to #if 0 when identifier hasn’t been defined, or has been undefined by the #undef directive. These directives check only for the presence or absence of identifiers defined with #define, not for identifiers declared in the C or C++ source code.
ifdef means if the following is defined while ifndef means if the following is not defined. So: #define one 0 #ifdef one printf(one is defined ); #endif #ifndef one printf(one is not defined ); #endif is equivalent to: printf(one is defined ); since one is defined so the ifdef is true and the ifndef is false.
#ifdef DEBUG /* Your debugging statements here */ #endif It tells the CPP to process the statements enclosed if DEBUG is defined. This is useful if you pass the -DDEBUG flag to the gcc compiler at the time of compilation. This will define DEBUG, so you can turn debugging on and off on the fly during compilation. Predefined Macros, Computer Programming – C Programming Language – #define and # ifdef in C programming language sample code – Build a C Program with C Code Examples – Learn C Programming Arrays Matrices … Program to check Vowel or Consonant using switch-case statement. I already explained in sample to print number of days in months, if switch case contains same …
Preprocessor Statements #ifdef, #else, #endif. These provide a rapid way to clip out and insert code. Consider; #define FIRST main() { int a, b, c;#ifdef FIRST a=2; b=6; c=4;#else printf(Enter a:); scanf(%d, &a); printf(Enter a:); scanf(%d, &a); printf(Enter a:);, #ifdef and #ifndef directives (C/C++) | Microsoft Docs, #ifdef in C# – Stack Overflow, #ifdef and #ifndef directives (C/C++) | Microsoft Docs, #ifdef and #ifndef directives (C/C++) | Microsoft Docs, #ifndef #ifndef /* code */ #else /* code to include if the token is defined */ #endif #ifndef checks whether the given token has been #defined earlier in the file or in an included file; if not, it includes the code between it and the closing #else or, if no #else is present, #endif statement.
4/11/2008 · # ifdef __cplusplus extern C {#endif what does it mean? C++ supports certain powerful but complex features that mean that different functions and variables can have different names: specifically, in C++ function names can be overloaded (two functions can have the same name, but different argument signatures), and also C++, 6/7/2017 · A Computer Science portal for geeks. It contains well written, well thought and well explained computer science and programming articles, quizzes and practice/competitive programming/company interview Questions.
C Preprocessor directives: Before a C program is compiled in a compiler, source code is processed by a program called preprocessor. This process is called preprocessing. Commands used in preprocessor are called preprocessor directives and they begin with “#” symbol. Below is the list of preprocessor directives that C programming language …
