Preprocessor directives are the text replacement tool, used to use in the program to replace the text by it value. The preprocessor provides the ability for the inclusion of header files, macro expansions, conditional compilation, and line control. All preprocessing work the subject of the rest of this manual is carried out in the source character set. Preprocessor directives in c tutorial 26 march 2020 learn. Module 10 preprocessor directives my training period. The c preprocessor is not a part of the compiler, but is a separate step in the compilation process. Covers topics like introduction to preprocessor directives, macro expansion, file inclusion, summary of preprocessor directives etc. Lets say we have a codebase that is used for many different costumers, and we have some code in it that is relevant only for costumers of type x. The c preprocessor provides the ability to perform macro substitution, conditional compilation, and inclusion of named files. For example, the c preprocessor sometimes outputs extra white space to avoid inadvertent c token concatenation, and this may cause problems with other languages. Y ou can split ev en an escap e sequence with bac kslashnewline. Yin lou 02092011 introduction to c cs 2022, spring 2011, lecture 8. The compiler and executable have no awareness that there is such a thing as a preprocessor. The preprocessor will process directives that are inserted into the c source code.
Feb 29, 2012 preprocessor directives are commands that are interpreted by the compiler and affect the output or behavior of the build process. Jan 31, 2018 processor directives like macro substitution, file inclusion and compiler control directives with examples. C programming course notes preprocessor directives. The c prepro cessor 1 1 the c prepro cessor the c prepro cessor is a macro pro cessor that is used automatically b y the c compiler to transform y our program b efore actual compilation. As soon as a newline character is found, the preprocessor directive is considered to end. Although the compiler doesnt have a separate preprocessor, the directives described in this section are processed as if there were one. Below is the list of preprocessor directives that c programming language. Whenever a cpp program is compiled then the following steps are taken. It is called micro preprocessor because it allows us to add macros. The c preprocessor is designed for c like languages. Most c preprocessor features are inactive unless you give specific directives to. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Preprocessor c multiple choice questions and answers. These preprocessor directives extend only across a single line of code.
The c preprocessor is a macro processor that is used automatically by the c compiler to. The preprocessor examines the code before actual compilation of code begins and resolves all these directives before any code is actually generated by. Preprocessor directives change the text of the source code and the result is a new source code without these directives. Lets take a small break from design patterns and learn a. This page lists the preprocessor directives, or commands to the preprocessor. Consult the manual or the reference of your compiler for more. Lines containing preprocessor directives can be continued by immediately preceding the endofline marker with a backslash \. In the past, it has been abused as a general text processor. Note that the macro will also fail for expressions x square62 if we want correct behavior from macro squarex, we should declare the macro as. In simplistic terms, a c preprocessor is just a text substitution tool and they instruct compiler to do required preprocessing before actual compilation. Preprocessor directives are lines included in the code of. It is called a macro processor because it allows you to definemacros, which are brief abbreviations for longer constructs. Preprocessor directives are lines included in the code of programs preceded. 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.
The preprocessor examines the code before actual compilation of code begins and resolves all these directives before any code is actually generated by regular statements. The effect of each preprocessor directive is a change to the text and the result is a transformation of the text that does not contain the directives nor comments. In many c implementations, it is a separate program invoked by the compiler as the first part of translation. Is it better to use preprocessor directives to inc. A number of the directives control conditional compilation, which allows certain portions of a program to be selectively compiled or ignored depending upon specified conditions. Preprocessor directives c programming developer insider. The preprocessor complicates debugging, because the debugger sees the preprocessor output, not source code input. C preprocessor directives are used only to instruct compilers.
For example, apostrophes will be interpreted as the beginning of character constants, and cause errors. Preprocessor directives are evaluated in a step called preprocessing couldnt have seen that coming, in which the prepro. Solved examples with detailed answer description, explanation are given and it would be easy to understand. The c preprocessor, often known as cpp, is a macro processor that is used automatically by the c compiler to transform your program before compilation. Preprocessor directives are nam preprocessor because preprocessor directives provide instructions to the compiler to preprocess the information before actual the compilation starts. Jan 12, 2018 preprocessor directives change the text of the source code and the result is a new source code without these directives. May 24, 2012 to include the various instructions to the compiler in the c source code,some directives are used called as preprocessor directives. It is called a macro processor because it allows you to define macros, which are brief abbreviations for longer constructs the c preprocessor provides four separate facilities that you can use as you see fit. Whenever a variable is used in the program, compiler understands it as a value stored in some memory address. A preprocessor directive must be the only instruction on a line.
This is the c programming questions and answers section on c preprocessor with explanation for various interview, competitive examination and entrance test. For example, normally the c preprocessor does not preserve arbitrary whitespace. It is called a macro processor because it allows you to define macros, which are brief abbreviations for longer constructs. Before a c program is compiled in a compiler, source code is processed by a program called preprocessor.
The preprocessor is executed before the actual compilation of code begins, therefore the preprocessor digests all these. This manual describes the behavior of the iso preprocessor. The preprocessor provides the ability for the inclusion of header files, macro expansions, conditional compilation, and line control in many c implementations, it is a separate program invoked by the compiler as the first part of translation the language of preprocessor directives is only. Aug 06, 2016 preprocessor directives, answers is also in this word.
Preprocessor replaces square6 by 66 and the expression becomes x 3666 and value of x is calculated as 36. Preprocessor directives preprocessor directives are lines included in the code of our programs that are not program statements but directives for the preprocessor. C preprocessor directives tutorial to learn c preprocessor directives in simple, easy and step by step way with syntax, examples and notes. Preprocessor directives allow you to make automatic changes to the code the compiler sees. Preprocessor directives, answers is also in this word. The book begins with an introduction to programming often adopted by an in depth introduction to c programming. It then delves into a whole analysis of various constructs of c akin to willpower control and looping statements, options, arrays, strings, pointers, development and union, file administration, and preprocessor directives. These lines are not program statements but directives for the preprocessor. The c preprocessor gcc, the gnu compiler collection. C preprocessor directives types of preprocessor directives. The preprocessor is executed before the actual compilation of code begins, therefore the preprocessor digests all these directives before any code is generated by the statements.
The preprocessor is a utility program, which processes special instructions that can be or are written in a c cpp program. The pli preprocessor is the preprocessor for the pli computer programming language. To include the various instructions to the compiler in the c source code,some directives are used called as preprocessor directives. Each preprocessor directive have different task which executes just before the actual execution of c program which makes the program more portable. Below is the list of preprocessor directives that c programming language offers. The c preprocessor 1 1 the c preprocessor the c preprocessor is a macro processor that is used automatically by the c compiler to transform your program before actual compilation. The first step in compiling any c program is the preprocessor, a sort of automated editor that modifies a copy of the source code before passing it on to the compiler to translate into machine language code one of the tasks of the preprocessor is to strip off all comments, which the compiler ignores. It will choke on input which does not obey cs lexical rules. Preprocessor directives can appear anywhere in a source file, but they apply only to the rest of the source file, after they appear.
This modification is done according to the preprocessor directives that are. Proprocessor direcives are executed before compilation. The following aspects of the preprocessor can be controlled. The c preprocessor is a micro processor that is used by compiler to transform your code before compilation. The c preprocessor is a macro processor that is used automatically by the c compiler to transform your program before actual compilation. Compiling a c program behind the scene a preprocessor is a system software a computer program that is designed to run on computers hardware and application programs. This macro is used to include a header file into the source file. Preprocessor programs provide preprocessors directives which tell the compiler to preprocess the source code before compiling. There are number of preprocessor directives supported. The preprocessor interprets a subset of the full pli language to perform source file inclusion, conditional compilation, and macro expansion. Top the c preprocessor gcc, the gnu compiler collection. The c preprocessor is not part of the compiler, but is a separate step in the compilation process. These directives allow additional actions to be taken on the c source code before it is compiled into object code.
Preprocessor directives are orders that we include within the code of our programs that are not instructions for the program itself but for the preprocessor. These commands specifies which sections of the code to compile or how to handle specific errors and warnings. In actuality, all of the preprocessor directives and macros have been fully expanded before the code is compiled. The preprocessor is a utility program, which processes special instructions that can be or are written in a ccpp program. Index of directives the c preprocessor gnu project. Preprocessor directives in c preprocessor directives in c courses with reference manuals and examples pdf. In simple terms, a c preprocessor is just a text substitution tool and it instructs the compiler to do required preprocessing before the actual compilation. It means that something need to be done before any processing compilation starts.
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