What is Ifndef in Verilog?

The keyword `ifndef simply tells the compiler to include the piece of code until the next `else or `endif if the given macro called FLAG is not defined using a `define directive.

What does #ifndef Mean?

#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.

Why do we use Ifndef?

#ifndef is often used to make header files idempotent by defining a token once the file has been included and checking that the token was not set at the top of that file.

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.

Is Ifndef a macro?

Explanation of #ifndef in C syntax: #ifndef MACRO: The #ifndef works for the opposite condition of the #ifdef directive of the C Programming Language. The “MACRO” definition should not be defined for the specific preprocessor which is used to include the C Programming Source Code into the specific compiled application.

What is macro in UVM?

Utility Macros. The utils macro is used primarily to register an object or component with the factory and is required for it to function correctly. It is required to be used inside every user-defined class that is derived from uvm_object which includes all types of sequence items and components.

Can we use #else for #ifdef?

The #elif is functionally equivalent to the #elseif directive. These directives are interchangeable.

What is the ifndef keyword in Verilog?

The keyword `ifndef simply tells the compiler to include the piece of code until the next `else or `endif if the given macro called FLAG is not defined using a `define directive. Note that by default, rstn will not be included during compilation of the design and hence it will not appear in the portlist.

What are the conditional compiler directives in Verilog?

Verilog has following conditional compiler directives. The `ifdef compiler directive checks for the definition of a text_macro_name. If the text_macro_name is defined, then the lines following the `ifdef directive are included. If the text_macro_name is not defined and an `else directive exists, then this source is compiled.

How are the ifdef and ifndef directives used?

`ifdef, `ifndef, `else, `endif ¶ Sections of code can be conditionally ignored using the `ifdef and `ifndef directives. It takes a macro name as an argument. With `ifdef the text that follows is ignored up to a matching `else or `endif if the argument is undefined and accepted otherwise.

When to use ElseIf, ifndef, and endif?

The #elseif, #else, and #endif directives are valid only following a #ifdef directive. If the #ifdef directive evaluated to be true, t hen these directives ( #elseif, #else, and #endif ) stop processing of the input lines until a #endif directive is encounter.