What does Ifdef mean?
if the following is defined
ifdef means “if the following is defined” while ifndef means “if the following is not defined”.
What is Ifdef in C programming?
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 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 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.
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 does Ifdef mean 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.
Can Ifdef be nested?
#ifdef directives can be nested, however, all directives in a given logical level must exist in a single file. The following sample code showing use of the #ifdef directive chain with nested #ifdefs. These directives are interchangeable.
What is a compiler directive like include and Ifdef *?
You can use the `undef compiler directive to undefine a text macro that you use in more than one file. Optionally includes lines of source code during compilation. The `ifdef directive checks that a macro has been defined, and if so, compiles the code that follows.
When to use the defined operator in ifdef?
Conditional Compilation You can use the defined operator in the #if directive to use expressions that evaluate to 0 or 1 within a preprocessor line. This saves you from using nested preprocessing directives. The parentheses around the identifier are optional.
What is the ifdef directive in C used for?
It is a define directive in C which checks if a MACRO has been defined previously or not. If it has been defined, it will define more MACROs and other statements. It is used for conditional compilation.
How to check if a condition is true in ifdef?
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’s the difference between if and ifndef in Java?
The defined( identifier ) constant expression used with the #if directive is preferred. The #ifndef directive checks for the opposite of the condition checked by #ifdef. If the identifier has not been defined, or if its definition has been removed with #undef, the condition is true (nonzero). Otherwise, the condition is false (0).