What does Ifdef mean in C++?
#ifdef: This directive is the simplest conditional directive. This block is called a conditional group. The controlled text will get included in the preprocessor output iff the macroname is defined. The controlled text inside a conditional will embrace preprocessing directives.
What is a preprocessor directive C++?
Preprocessor directives are lines included in the code of programs preceded by a hash sign ( # ). The preprocessor examines the code before actual compilation of code begins and resolves all these directives before any code is actually generated by regular statements.
What does #endif mean in C++?
The #if directive, with the #elif, #else, and #endif directives, controls compilation of portions of a source file. If the expression you write (after the #if) has a nonzero value, the line group immediately following the #if directive is kept in the translation unit.
What does Ifndef mean in C?
Description. In the C Programming Language, the #ifndef directive allows for conditional compilation. The preprocessor determines if the provided macro does not exist before including the subsequent code in the compilation process.
How do I use Ifdef in CPP?
#ifdef means if defined. If the symbol following #ifdef is defined, either using #define in prior source code or using a compiler command-line argument, the text up to the enclosing #endif is included by the preprocessor and therefore compiled. #if works similarly, but it evaluates the boolean expression following it.
Where is Ifdef defined?
In the C Programming Language, the #ifdef directive allows for conditional compilation. The preprocessor determines if the provided macro exists before including the subsequent code in the compilation process.
What are pre processor directives give two examples?
Examples of some preprocessor directives are: #include, #define, #ifndef etc. Remember that # symbol only provides a path that it will go to the preprocessor, and command such as include is processed by preprocessor program. For example, include will include extra code to your program.
What is the preprocessor directive which is used to end the scope of #ifdef?
#endif
#endif is used to end the scope of #ifdef.
What is Ifdef and Ifndef?
ifdef means “if the following is defined” while ifndef means “if the following is not defined”.
What is the difference between #if and #ifdef?
#if checks for the value of the symbol, while #ifdef checks the existence of the symbol (regardless of its value).
What is the use of ifdef in C++?
#ifdef. #ifdef /* code */ #else /* code to include if the token is not defined */ #endif ifdef checks whether the given token has been #defined earlier in the file or in an included file. If so, it includes everything between it and the closing #else or, if no #else is present, the closing #endif.
What is a preprocessor directive in C programming?
The C preprocessormodifies a source file before handing it over to the compiler, allowing conditional compilation with #ifdef, defining constants with #define, including header files with #include, and using builtin macros such as __FILE__. This page lists the preprocessor directives, or commands to the preprocessor, that are available:
What are the if-else directives for conditional compilation?
The if-else directives #if, #ifdef, #ifndef, #else, #elif and #endif can be used for conditional compilation. Most compilers targeting Microsoft Windows implicitly define _WIN32. This allows code, including preprocessor commands, to compile only when targeting Windows systems. A few compilers define WIN32 instead.
What is the difference between ifdef and ifndef in PHP?
The #ifndef directive is simply opposite to that of the #ifdef directive. In case of #ifndef, the block of statements between #ifndef and #endif will be executed only if the macro or the identifier with #ifndef is not defined.