What is else of #ifdef?

If an #ifdef is evaluated to be false, then the #elseif directive is processed as if it was an #ifdef directive. If all #elseif directives evaluate to be false, the #else directive is processed if it exists. Input is evaluated until an #endif directive is encountered.

What is ifdef and endif?

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 …

What does Ifdef mean?

#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.

Can Ifdef be nested?

`ifdef and its flavors can be nested one inside the other to create complex ways of code inclusion and exclusion with defined macros.

What is the difference between Ifdef and if defined?

If the identifier is not defined, it evaluates to 0. On the other hand, #ifdef can only be followed by an identifier. If the identifier is defined, i.e., the identifier is actually a macro, the code below it is compiled.

How do I use Ifdef in CPP?

The #ifndef directive checks for the opposite of the condition checked by #ifdef . If the identifier hasn’t been defined, or if its definition has been removed with #undef , the condition is true (nonzero). Otherwise, the condition is false (0). The identifier can be passed from the command line using the /D option.

What is ifdef and endif in C++?

#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.

What does endif mean?

Noun. endif (plural endifs) (computing) A directive, in several programming languages, that marks the end of an if statement, especially one containing multiple if then else statements.

What is difference between #if and #ifdef?

You can use the #ifdef and #ifndef directives anywhere #if can be used. 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.

What is #ifndef #define and #endif used for?

#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 language uses endif?

C Programming Language
In the C Programming Language, the #endif directive is used to define the following directives: #if, #ifdef , and #ifndef . Whenever the #endif directive is encountered in a program, it determines if the preprocessing of #if, #ifdef, or #ifndef has been completed successfully.

Is endif a keyword?

The endif keyword is used to mark the end of an if conditional which was started with the if(…): syntax. It also applies to any variation of the if conditional, such as if…