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.

What does Ifdef mean?

ifdef means "if the following is defined" while ifndef means "if the following is not defined".

What is the purpose of #ifndef?

#ifndef and #define are known as header guards. Their primary purpose is to prevent C++ header files from being included multiple times.

What are macros in C programming?

A macro is a piece of code in a program that is replaced by the value of the macro. Macro is defined by #define directive. Whenever a macro name is encountered by the compiler, it replaces the name with the definition of the macro.

What is Ifndef and 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.

What is ifdef and endif in C?

#ifdef: This directive is the simplest conditional directive. ... They are executed only if the conditional succeeds. You can nest these in multiple layers, but they must be completely nested. In other words, '#endif' always matches the nearest '#ifdef' (or '#ifndef', or '#if').

What is #if and #endif 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 is macro in embedded C?

A macro is a fragment of code which has been given a name. Whenever the name is used, it is replaced by the contents of the macro. ... Object-like macros resemble data objects when used, function-like macros resemble function calls. You may define any valid identifier as a macro, even if it is a C keyword.

Why macros are used in C?

In C, the macro is used to define any constant value or any variable with its value in the entire program that will be replaced by this macro name, where macro contains the set of code that will be called when the macro name is used in the program.

What is the difference between #ifdef and #ifndef?

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. ... The #ifndef directive checks for the opposite of the condition checked by #ifdef .

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 pragma in C?

A pragma instructs the compiler to perform a particular action at compile time. Pragmas vary from compiler to compiler. For example, you can use the optimize pragma to set the optimizations to perform on your program. The Microsoft C pragmas are: alloc_text.

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.

What is Ifndef online judge?

Generally this flag is used in order for the code to read & write from a file rather than stdin when run on a local machine and read & write from stdin and stdout respectively when run in an online judge. Thus it eliminates the need to edit the code, for reading from a file, and again for reading from stdin.

What is extern C?

extern "C" is a linkage specification which is used to call C functions in the Cpp source files. We can call C functions, write Variables, & include headers. Function is declared in extern entity & it is defined outside.

What is a macro example?

Macro is defined as something that covers a large amount, or is large in size. An example of macro is the study of the key driving aspects of an economy; macro economics. An example of macro is a very close up photograph of an ant; a macro photograph.

What is the purpose of macros?

Macros are programs used to automate frequently used processes or tasks in Excel. A macro records operations and re-uses the sequence of mouse actions or keystrokes of anything you can do in Excel with keystrokes or a mouse.

Where macros are stored in C?

Macros are not stored in memory anywhere in the final program but instead the code for the macro is repeated whenever it occurs. As far as the actual compiler is concerned they don't even exist, they've been replaced by the preprocessor before they get that far.

What is macro substitution in C?

The macro substitution is a process where an identifier in a program is replaced by a predefined string or a value. Different forms of macro substitution: ... Simple macro substitution.

What is #if in C?

Description. In the C Programming Language, the #if directive allows for conditional compilation. The preprocessor evaluates an expression provided with the #if directive to determine if the subsequent code should be included in the compilation process.

What is end if statement?

Description: The endif command is used to terminate a multiple line if command. The command can either be specified as a single word, 'endif' or as two separate words, 'end if'.

Where do I put endif?

Like other conditional directives, if the condition is true then the statements between the #ifndef and an #endif will be used in the program. is placed at the end of the file. at the beginning of the header file to be protected and #endif /* unique_symbol*/ at the end of the header file.

How do you define else if?

Alternatively referred to as elsif, else if is a conditional statement performed after an if statement that, if true, performs a function.

What is Ifdef Verilog?

The keyword `ifdef simply tells the compiler to include the piece of code until the next `else or `endif if the given macro called FLAG is defined using a `define directive.