The c preprocessor modifies a source file before handi. In simplistic terms, a c preprocessor is just a text substitution tool and they instruct compiler to do required preprocessing before actual compilation. The c preprocessor is a macro processor that is used automatically by the c compiler to transform your program before actual compilation. C programming language tutorial c language preprocessor. Read the book online, print the pdf, or buy a copy of the book. Learn c programming pdf free ebook for beginners the. File inclusive directives file inclusive directories are used to include user define header file inside c program. Most c preprocessor features are inactive unless you give specific directives to.
Generally, the optionalconditional compilation symbols will be provided by the build script. The conditional compilation directive statements define, undefine, if, elseif, else, endif, and eof allow you to select or omit. C tutorial for beginners with examples learn c language covering basic c, literals, data types, functions, c preprocessors, directives etc. Two notable users of this directive are openmp and openacc. Below is the list of preprocessor directives that c programming language. This page lists the preprocessor directives, or commands to the preprocessor. This directive has been used assiduously in other sections of this tutorial. The c preprocessor gcc, the gnu compiler collection.
File inclusive directives c preprocessor directives c. Tutorialspoint online c tutorial interactive online version tutorialspoint printed c tutorial download pdf version. The preprocessor is executed before the actual compilation of code begins, therefore the preprocessor digests all these directives before any code is. Special functions have been designed for handling file operations. In the first phase, a tool called the preprocessor scans the human written source code and converts it to compiler friendly content and format. They are almost completed so i thought that i should combine all those tutorials at one place and make an ebook. File inclusive directory checks included header file inside same directory if path is not mentioned. Note that the preprocessor directives are specified in a single line of code and they dont need an ending semicolon. 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 preprocessor is a utility program, which processes special instructions that can be or are written in a ccpp program. For simple programs which do not return any value, we use void main, like this. The preprocessor is executed before the actual compilation of code begins, therefore the preprocessor digests all these.
A is copied into the parameter a, b into b, c into c, and x into x, and then the function executes. Conditional preprocessor directives evaluate constant integer expressions. The ones that cannot be evaluated in preprocessor directives are sizeof expressions and enumeration constants. A preprocessor directive must be the only instruction on a line. Preprocessor directives must be the first nonwhitespace text specified on a line. Preprocessor directives are lines included in the code of programs preceded by. This tutorial is a quick, easy and fairly concise, interactive online tutorial for learning the syntax of the c language. Preprocessor directives provide support for inclusion of header files, macro expansions, conditional compilation, and line control. C programming course notes preprocessor directives. The online version allows you to immediately compile code fragments to see their behavior, and the pdf version is easily read on your desktop, cell phone.
Preprocessing and macros c preprocessor preprocessor directives. But i want to give you a link to a simple sample found at microsofts msdn. Preprocessor directives preprocessor directives are lines included in the code of our programs that are not program statements but directives for the preprocessor. The preprocessing language consists of directives to be executed and macros to be ex panded. Preprocessor directives are not statements, so they do not end with a semicolon. The compiler works through the preprocessor directives first, making substitutions, inclusions, and even decisions before the source code is translated into object code. One common use of the preprocessor directive is in the inclusion of a header file. Before a c program is compiled in a compiler, source code is processed by a program called preprocessor. Permission is granted to make and distribute verbatim copies of this manual.
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. In the second phase the compiler generates object code usually in the form of file with a. These lines are not program statements but directives for the preprocessor. Opening a file before we perform any operations on a file, we need to open it. Preprocessing directives sun workshop compiler c 5. The programming language of preprocessor directives is agnostic to the grammar of c, thus the c preprocessor could likewise be employed.
When it returns, the avlue that it returns is used in the caller wherever the call was written. 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. A preprocessor directive is given to the compiler before the c code is compiled. Learning the c programming language mosaic industries. The c preprocessor modifies a source code file before handing it over to the compiler. Preprocessor directives preprocessor directives are not program statements but directives for the preprocessor. I often use such conditions to handle code that must run on different runtimes mono, cf, silverlight, etc. The computer will begin executing your program from the main function. Preprocessing directives are lines in your program that start with.
Programming fundamentals a modular structured approach. What are the functions of preprocessor directives in c. 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. In various c executions, it is a discriminate program raised by the compiler as the first constituent of translation. In this tutorial, you will be introduced to c preprocessors, and you will learn to use. The c preprocessor is not part of the compiler, but is a separate step in the compilation process.
This section describes assertions, pragmas, and predefined names. Whenever a cpp program is compiled then the following steps are taken. No semicolon is expected at the end of a preprocessor directive. The first four phases of translation assigned in the c standard are. Use of the preprocessor is advantageous since it makes. The compiler directive statements title, eject, space, copy, and include allow you to specify heading information for the compiler listing, to control the spacing of the compiler listing, and to insert records from other file members during a compile. In general terms the compilation of objectivec programs from source code to executable binary is a three phase process. Preprocessor directives are lines included in the code of. Postscript or pdf produced by some word processors for output purposes only. Preprocessor directives are lines included in the code of our programs that are not program statements but directives for the preprocessor. The compiler expects the preprocessor to be a single line of code. The header files are stored in the c library, which comes with your compiler. I have no guru statement regarding to the usage of preprocessor directives in my mind and can not add a reference to a famous one.
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