What is a conditional directive?
A conditional is a directive that instructs the preprocessor to select whether or not to include a chunk of code in the final token stream passed to the compiler.
What are different conditional compilation directives?
The directives are: The #if and #elif directives, which conditionally include or suppress portions of source code, depending on the result of a constant expression. The #ifdef directive, which conditionally includes source text if a macro name is defined. The #endif directive, which ends conditional text.
What is the difference between Ifdef and Ifndef?
ifdef means “if the following is defined” while ifndef means “if the following is not defined”. since that specifies the intent more clearly in this particular situation.
What is #if and #endif?
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.
How do you do a conditional directive?
Currently, there is NO way to conditionally apply a directive to a component. This is not supported. The components which you have created can be added or removed conditionally.
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 is meant by conditional compilation?
In computer programming, conditional compilation is compilation implementing methods which allow the compiler to produce differences in the executable program produced and controlled by parameters that are provided during compilation.
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 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 is the purpose of #ifndef and its associated #define and #endif?
Which of the following is an attribute directive?
The attribute directive changes the appearance or behavior of a DOM element. The ngModel directive which is used for two-way is an example of an attribute directive. Some of the other attribute directives are listed below: NgSwitch: It is used whenever you want to display an element tree consisting of many children.
What all directives are there in angular?
There are four types of directives in Angular,
- Components directives.
- Structural directives.
- Attribute directives.
- Custom Directive.
How do I apply a directive conditionally?
This may come late, but it is a viable and elegant method for applying a directive conditionally. When applying the directive, set the apply property of the input variable: In the method of the directive check for the variable this.options.apply and apply the directive logic based on the condition:
What is the difference between condition and condition in ifndef directive?
If the given argument is true then condition becomes true. The ifndef directive begins the conditional, and specifies the condition. It contains single argument. If the given argument is false then condition becomes true.
What are the preprocessor directives in C?
C preprocessor directives – #include, #define, #undef and conditional directives. A C preprocessor is a statement substitution (text substitution) in C programming language. It instructs the C compiler to do some specific (required) pre-processing before the compilation process.
What is the difference between IF statement and preprocessing conditional directive?
The condition in an if statement is tested during the execution of your program. Its purpose is to allow your program to behave differently from run to run, depending on the data it is operating on. The condition in a preprocessing conditional directive is tested when your program is compiled.