Preprocessor directives are lines included in the code of programs preceded. For example, normally the c preprocessor does not preserve arbitrary whitespace. This macro is used to include a header file into the source file. Solved examples with detailed answer description, explanation are given and it would be easy to understand. May 24, 2012 to include the various instructions to the compiler in the c source code,some directives are used called as preprocessor directives. The preprocessor examines the code before actual compilation of code begins and resolves all these directives before any code is actually generated by. 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. Lets take a small break from design patterns and learn a.
Preprocessor c multiple choice questions and answers. Preprocessor directives change the text of the source code and the result is a new source code without these directives. 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. Learn vocabulary, terms, and more with flashcards, games, and other study tools. For example, the c preprocessor sometimes outputs extra white space to avoid inadvertent c token concatenation, and this may cause problems with other languages. Preprocessor directives are lines included in the code of.
These directives allow additional actions to be taken on the c source code before it is compiled into object code. 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. In simplistic terms, a c preprocessor is just a text substitution tool and they instruct compiler to do required preprocessing before actual compilation. It is called a macro processor because it allows you to define macros, which are brief abbreviations for longer constructs. 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. Preprocessor directives are evaluated in a step called preprocessing couldnt have seen that coming, in which the prepro. Whenever a cpp program is compiled then the following steps are taken. Is it better to use preprocessor directives to inc. Module 10 preprocessor directives my training period. The c preprocessor is not part of the compiler, but is a separate step in the compilation process.
The compiler and executable have no awareness that there is such a thing as a preprocessor. Preprocessor directives are the text replacement tool, used to use in the program to replace the text by it value. The c preprocessor is designed for c like languages. It is called a macro processor because it allows you to definemacros, which are brief abbreviations for longer constructs. Lines containing preprocessor directives can be continued by immediately preceding the endofline marker with a backslash \. The pli preprocessor is the preprocessor for the pli computer programming language. 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.
The c preprocessor provides the ability to perform macro substitution, conditional compilation, and inclusion of named files. Yin lou 02092011 introduction to c cs 2022, spring 2011, lecture 8. A preprocessor directive must be the only instruction on a line. For example, apostrophes will be interpreted as the beginning of character constants, and cause errors. Below is the list of preprocessor directives that c programming language. All preprocessing work the subject of the rest of this manual is carried out in the source character set. In the past, it has been abused as a general text processor. 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. The c preprocessor is a macro processor that is used automatically by the c compiler to transform your program before actual compilation. 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.
The c preprocessor is not a part of the compiler, but is a separate step in the compilation process. In many c implementations, it is a separate program invoked by the compiler as the first part of translation. 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. 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. Preprocessor directives in c preprocessor directives in c courses with reference manuals and examples pdf. 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. C preprocessor directives are used only to instruct compilers. 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. This page lists the preprocessor directives, or commands to the preprocessor. 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. Preprocessor directives c programming developer insider. In actuality, all of the preprocessor directives and macros have been fully expanded before the code is compiled. Whenever a variable is used in the program, compiler understands it as a value stored in some memory address.
It is called micro preprocessor because it allows us to add macros. The c preprocessor is a macro processor that is used automatically by the c compiler to. C preprocessor directives types of preprocessor directives. Proprocessor direcives are executed before compilation. There are number of preprocessor directives supported. Jan 31, 2018 processor directives like macro substitution, file inclusion and compiler control directives with examples. The preprocessor is a utility program, which processes special instructions that can be or are written in a ccpp program. Before a c program is compiled in a compiler, source code is processed by a program called preprocessor. Preprocessor replaces square6 by 66 and the expression becomes x 3666 and value of x is calculated as 36. Below is the list of preprocessor directives that c programming language offers. Jan 12, 2018 preprocessor directives change the text of the source code and the result is a new source code without these directives. Preprocessor directives, answers is also in this word. The c preprocessor gcc, the gnu compiler collection.
It will choke on input which does not obey cs lexical rules. Feb 29, 2012 preprocessor directives are commands that are interpreted by the compiler and affect the output or behavior of the build process. These commands specifies which sections of the code to compile or how to handle specific errors and warnings. This is the c programming questions and answers section on c preprocessor with explanation for various interview, competitive examination and entrance test. Covers topics like introduction to preprocessor directives, macro expansion, file inclusion, summary of preprocessor directives etc. Most c preprocessor features are inactive unless you give specific directives to. The c preprocessor is a micro processor that is used by compiler to transform your code before compilation. Preprocessor directives in c tutorial 26 march 2020 learn. To include the various instructions to the compiler in the c source code,some directives are used called as preprocessor directives. It means that something need to be done before any processing compilation starts. The preprocessor will process directives that are inserted into the c source code. Top the c preprocessor gcc, the gnu compiler collection. The book begins with an introduction to programming often adopted by an in depth introduction to c programming.
Although the compiler doesnt have a separate preprocessor, the directives described in this section are processed as if there were one. C preprocessor directives tutorial to learn c preprocessor directives in simple, easy and step by step way with syntax, examples and notes. Preprocessor directives preprocessor directives are lines included in the code of our programs that are not program statements but directives for the preprocessor. The preprocessor is executed before the actual compilation of code begins, therefore the preprocessor digests all these. 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 manual describes the behavior of the iso preprocessor. Preprocessor programs provide preprocessors directives which tell the compiler to preprocess the source code before compiling.
These lines are not program statements but directives for the preprocessor. 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. Y ou can split ev en an escap e sequence with bac kslashnewline. 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 can appear anywhere in a source file, but they apply only to the rest of the source file, after they appear.
Each preprocessor directive have different task which executes just before the actual execution of c program which makes the program more portable. The preprocessor interprets a subset of the full pli language to perform source file inclusion, conditional compilation, and macro expansion. The preprocessor complicates debugging, because the debugger sees the preprocessor output, not source code input. Preprocessor directives are nam preprocessor because preprocessor directives provide instructions to the compiler to preprocess the information before actual the compilation starts. 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. C programming course notes preprocessor directives. Preprocessor directives allow you to make automatic changes to the code the compiler sees.
Consult the manual or the reference of your compiler for more. The following aspects of the preprocessor can be controlled. The preprocessor provides the ability for the inclusion of header files, macro expansions, conditional compilation, and line control. This modification is done according to the preprocessor directives that are. 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 preprocessor is a utility program, which processes special instructions that can be or are written in a c cpp program. Aug 06, 2016 preprocessor directives, answers is also in this word. These preprocessor directives extend only across a single line of code.
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