Max macro in c1/14/2024 The compiler gives fatal error if #error directive is found and skips further compilation process. The #error preprocessor directive indicates error. It can be used with #if, #elif, #ifdef and #ifndef directives. The #else preprocessor directive evaluates the expression or condition if condition of #if is false. If condition is true, it executes the code. The #if preprocessor directive evaluates the expression or condition. The #ifndef preprocessor directive checks if macro is not defined by #define. The #ifdef preprocessor directive checks if macro is defined by #define. Output: Compile Time Error: 'PI' undeclared The function-like macro looks like function call. Let's see an example of Object-like Macros : #include Here, PI is the macro name which will be replaced by the value 3.14. It is widely used to represent numeric constants. The object-like macro is an identifier that is replaced by value. Let's start with macro, as we discuss, a macro is a segment of code which is replaced by the value of macro. Any #include directive whose argument does not fit the above two forms is a computed include. This variant is called a computed #include. The current directory is the directory of the current input file. It searches for a file named file first in the current directory, then in the same directories used for system header files. This variant is used for header files of your own program. It searches for a file named file in a list of directories specified by you, then in a standard list of system directories. This variant is used for system header files. If included file is not found, compiler renders error. It is used include system-defined and user-defined header files. The #include preprocessor directive is used to paste code of given file into current file. For example, if foo is defined as a macro expanding to define, that does not make #foo a valid preprocessing directive.Īll preprocessor directives starts with hash # symbol. The # and the directive name cannot come from a macro expansion. Whitespace is also allowed before and after the #. For example, #define is the directive that defines a macro. The # is followed by an identifier that is the directive name. Preprocessing directives are lines in your program that start with #. A macro is a segment of code which is replaced by the value of macro. It is called a macro processor because it allows you to define macros, which are brief abbreviations for longer constructs. The C preprocessor is a macro processor that is used automatically by the C compiler to transform your program before actual compilation (Proprocessor direcives are executed before compilation.).
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