pre processor directives in C
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pre processor directives in C

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pre processor directives in C pre processor directives in C Presentation Transcript

  • PREPROCESSORS IN C BY SAHITHI NARAPARAJU
  • INTRODUCTION:  One of the unique feature of C language is preprocessor.  The preprocessor is a program that processes the source code before it passes through compiler.  Pre processor directives are divided into 3 categories: 1. Macro substitution directives 2. File inclusion directives 3. Compiler control directives
  • MACRO SUBSTITUTION :  Macro substitution is a process where an identifier in a program replaced by predefined string composed of one or more tokens.  It is achieved by #define directive. FILE INCLUSION :  An external file containing functions or macro definition can be included as apart of program so that we need not rewrite those function or macro definition.  This is achieved by #include directive.
  • ADDITIONAL PREPROCESSOR DIRECTIVES #ELIF DIRECTIVE: #ELIF enables us to establish an if else if sequence for testing multiple conditions.  #PRAGMA DIRECTIVE: #PRAGMA is an implementation oriented directive that allows us to specify various instructions to be given to compiler. Syntax: #pragma name 
  • #ERROR : #ERROR directive is used to produce diagnostic messages during debugging. Syntax: #error error message. 
  • PREPROCESSOR OPERATORS There are 2 preprocessor operations namely: 1. Stringizing operator # 2. Token pasting operator ##  Stringizing operator #: It is used in definition of macro functions. This operator allows a formal argument within a macro definition to be converted to a string. Syntax: #define sum(XY)printf(#xy”=%fn”,xy); 
  • Token pasting operator ##:  The token pasting operator enables us to combine two tokens within a macro definition to form a single token. Syntax: #define combine(string1,string2) s1##s2.