C/C++ Training

Programming C/C++ on Eclipe

Trình bày: Ths HungNM

      Introduction preprocessor.

Preprocessing Logical Preprocessor Directives Standard Preprocessing Macros Error Generation Using the assert() Macro

The Preprocessor

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Introduction preprocessor

    The preprocessor is powerful tool.

It also can be a source of hard-to-find bugs.

It can be easily be misused to create program that are almost impossible to understand.

The preprocessor is controlled by processing directive that begin a # character.

C Program

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Preprocessing

  Including Header Files  A header file is any external file whose contents   It use of the #include preprocessor directive.

Syntax : • #include External Variables and Functions  A program that’s made up of several source files    want to use a global variable that’s defined in another file.

Declaring the variable as external to the current file using the extern keyword.

Syntax : • extern datatype namevariable; • Example : extern int number;

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Preprocessing

 Macro definition.

    The #define directive defines a macro.

The #undefine directive remove a macro definition. Syntax : • #define identifer replacement-list Example : • #define PI 3.14159265

• #define Black White  Advance macro definition.

• It make program easier to read.

• It make program easier to modify • It help avoid inconsistencies and topographical error.

– Example : Numerical constant like : 3.14149, but some time 3.1415

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Preprocessing

 Macro definition.

 Advance macro definition • Making minor changes to syntax of C program.

– Example : #define BEGIN { – #define END } • Renaming types.

– Exampe : #define BOOL int • Controlling conditional compilation.

– Example : #define DEBUG

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Preprocessing

 Macros That Look Like Functions    Allows parameters to be specified, which may themselves be replaced by argument values, Syntax : • #define identifer(x1,x2,..,xn) replacement list Example : • #define max(x, y) x>y ? x : y • Call : result = myval>99 ? myval : 99; • It mean : result = max(myval, 99);

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Preprocessing

  Preprocessor Directives on Multiple Lines  using the statement continuation character, \.

 Example : • #define min(x, y) \ ((x)<(y) ? (x) : (y)) Strings As Macro Arguments  Example: #define MYSTR "This string"  Call : printf("%s", MYSTR);

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Preprocessing

 Joining Two Results of a Macro Expansion    you may wish to generate two results in a macro and join them together Using two characters ## serves to separate the parameters.

Syntax : • #define join(a, b) a##b  Example : • strlen(join(var, 123)); • It will be result : strlen(var123);

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Logical Preprocessor Directives

 Conditional Compilation   Syntax : #if defined identifier #endif Or  #if !defined identifier #endif Or #if !defined block1 #define block1 /* Block of code you do not */ /* want to be repeated. */ #endif

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Logical Preprocessor Directives

 Directives Testing for Specific Values   Using #if directive expression.

Syntax : to test the value of a constant #if constant_expression #endif  Example : #if CPU == Pentium4 printf("\nPerformance should be good." ); #endif

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Logical Preprocessor Directives

 Multiple-Choice Selections    Using #if, #elseif, #else derective for excecute statements.

Syntax : #if constant_expression #elseif constant_expression #elseif constant_expression #else #endif Example : #if CPU == Pentium4 printf("\nPerformance should be good." ); #else printf("\nPerformance may not be so good." ); #endif

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Standard Preprocessing Macros

      Using __DATE__ macro provides a string representation of the date.

Using __TIME__, provides a string containing the value of the time.

Using __FILE__ , A string literal containing the name of the file being compiled.

__LINE__ A decimal constant containing the current source line number. __STDC_VERSION__ : This macro expands to the C Standard's version number.

Example :  printf("\nProgram last compiled at %s on %s", __TIME__, __DATE__ );

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Error Generation

 A

preprocessor error directive

causes the preprocessor to generate an error message and causes the compilation to fail.

 Syntax :  # error token-sequence  Example : #define BUFFER_SIZE 255 #if BUFFER_SIZE < 256 #error "BUFFER_SIZE is too small." #endif generates the error message: BUFFER_SIZE is too small.

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Using the assert() Macro

  The assert() macro is defined in the standard library header file .

Using #ndefine derectives for Switch on or off assertions.

  Syntax: #undef NDEBUG #include Example: #undef NDEBUG #include #include int main(void) { int y = 5; for(int x = 0 ; x < 20 ; x++) { printf("\nx = %d y = %d", x, y); } assert(x

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End

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