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