Chapter 10 Preprocessor

1
Chapter 10 Preprocessor

• By C. Shing
• ITEC Dept
• Radford University

2
Objectives

• Understand predefined system macro
• Understand how to use macro with arguments

3
Macro

• Called in-line function
• Has separate name space (either upper
• or lower case) from function names
• More efficient than function for short
• function code

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Macro (Cont.)

• Types of macro
• include
• define, undef
• Coditional macro if, ifdef, ifndef
• error
• line linenumber
• Operators ,

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Macro (Cont.)

• Example
• define getchar() getc(stdin)
• define putchar(c) putc((c), stdout)
• define swap(xptr,yptr) int tmp tmpxptr \
• xptryptr yptrtmp

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Predefined System Macro

• Begins and end with two underscores
• __DATE__ current date
• __TIME__ current time
• __FILE__ current file name
• __LINE__ current line number

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Define Macro with Argument

• Do not leave space between macro and argument
• Do not put at the end of the macro definition
• Treat argument as an entity by putting () around
• argument
• Treat the whole result as an entity by putting ()
  
• around argument

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Define Macro with Argument (Cont.)

• Example
• define CUBE(x) ((x)(x)(x))
• if (i3)
• xCUBE(y2)
• else
• xy2
• The above code is expanded intp
• If (i3)
• x((y2)(y2)(y2))
• else
• xy2

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Cancel Macro Definition

• Cancel macro definition before redefine it
• Form undef (macroname)
• Example
• undef CUBE

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Conditional Macro

• Form
• if
• statements
• endif
• Or
• if
• statements
• elif
• statements
• else
• statements
• endif

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Conditional Macro (Cont.)

• Example
• if (y gt -2)
• xCUBE(y2)
• else
• xy2
• endif

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Conditional Macro (Cont.)

• Form (Cont.)
• ifdef
• ifndef or if !defined()

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Conditional Macro (Cont.)

• Example
• ifndef CUBE
• define CUBE(x) ((x)(x)(x))
• endif
• Or
• if !defined(CUBE)
• define CUBE(x) ((x)(x)(x))
• endif

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Conditional Macro (Cont.)

• Class Example
• Create a platform independent code
• Example1
• DOS Executable

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Error Macro

• Form error error message
• Example
• if (ylt-2)
• error Not allowed to calculate (y2)3
• endif

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Line Macro

• Form line linenumber filename.c
• Starts renumber using the linenumber to
  filename.c
• Example
• line 1000 renumbered_file.c

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Implementation Dependent Macro

• Form pragma tokens
• If token is in implentation, take action.
• Otherwise, ignore it.

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Operators ,

• format replaced by string
• Example
• define integer_addition(x, y) \
• printf(x y d,xy)
• inetger_addition(3,4) // print out 347

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Operators , (Cont.)

• merge tokens
• Example
• define Y(i) yi
• Y(1)Y(2)Y(3)Y(4)100
• // this produces y1y2y3y4100

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References

• Deitel Deitel C How to Program, 4th ed.,
• Chapter 13, Prentice Hall