C programming session6

C programming session6

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  C_Programming Part 6 ENG. KEROLESSHENOUDA 1
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  C – Preprocessordirectives  Before a C program is compiled in a compiler, source code is processed by a program called preprocessor. This process is called preprocessing.  Commands used in preprocessor are called preprocessor directives and they begin with “#” symbol. 2
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  A program inC language involves into different processes 3
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  DIFFERENCE BETWEEN COMPILERSVS INTERPRETERS IN C LANGUAGE? Compilers Interpreters Compiler reads the entire source code of the program and converts it into binary code. This process is called compilation. Binary code is also referred as machine code, executable, and object code. Interpreter reads the program source code one line at a time and executing that line. This process is called interpretation. Program speed is fast. Program speed is slow. One time execution. Example: C, C++ Interpretation occurs at every line of the program. Example: BASIC 4
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  list of preprocessordirectives that C programming language offers. Preprocessor Syntax/Description Macro Syntax: #define This macro defines constant value and can be any of the basic data types. Header file inclusion Syntax: #include <file_name> The source code of the file “file_name” is included in the main program at the specified place. Conditional compilation Syntax: #ifdef, #endif, #if, #else, #ifndef Set of commands are included or excluded in source program before compilation with respect to the condition. Other directives Syntax: #undef, #pragma #undef is used to undefine a defined macro variable. #Pragma is used to call a function before and after main function in a C program. 5
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  Macro 6 Sometimes programmersrepeat the writing of the same code segment all over the program. Sometimes the code segment is repeated exactly another times it repeated with some changes. If the repeated code size is large, it is preferable to define a function for this code. If the repeated code size is small Macros may be the best choice. Macros also do not affect the execution speed because there is no parameter passing in Macros.
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  Macro 7 Macros Is Text Replacement
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  Macro How To seethe .i file (precompiled file ) 8 First we will Modify the Project Settings To Compile not internally But from external Makefile
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  Macro How To seethe .i file (precompiled file ) 9 Second Run the Build and Then you will Find a Makefile will be created Automatically Kindly Note You will get full Knowledge on Makefile on the Next Sessiones
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  Macro How To seethe .i file (precompiled file ) 10 Third: This Makefile generated Automatically at Every time you build So if we want to Modify on it without any change Do the Following Unmark it
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  Macro How To seethe .i file (precompiled file ) 11 Fourth : we will add a commands to generate .i and .s By our hand on the Makefile
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  Macro How To seethe .i file (precompiled file ) 12 Fifth: Rebuild again You will see the files Generated
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  We can seethe precompiled file .i have a text replacement for MACRO 13 Now are you agree with me The #define directives define the identifier as a macro, that is they instruct the compiler to replace all successive occurrences of identifier with replacement-list
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  Another Example 14
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  Another Example 15
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  __VA_ARGS__  Version (3)of the #define directive defines a function-like macro with variable number of arguments. The additional arguments can be accessed using __VA_ARGS__ identifier, which is then replaced with arguments, supplied with the identifier to be replaced.  Version (4) of the #define directive defines a function-like macro with variable number of arguments, but no regular arguments. The arguments can be accessed only with __VA_ARGS__ identifier, which is then replaced with arguments, supplied with identifier to be replaced.  A ## operator between any two successive identifiers in the replacement-list runs parameter replacement on the two identifiers and then concatenates the result 16
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  Think in Depth howto overcome on this error without remove Dprintf from main 19 Two errors
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  Think in Depth howto overcome on this error without remove Dprintf from main 20 # Convert to string
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  #undef directive  The#undef directive undefines the identifier, that is it cancels the previous definition of the identifier by #define directive. If the identifier does not have an associated macro, the directive is ignored. 21
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  EXAMPLE PROGRAM FORUNDEF IN C LANGUAGE: 22
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  Think In Depth Tryto make function factory and use it by Macro  Use one macro to create two Functions, one responsible on multiply input argument to 4 and the other to multiply one input argument to 2.  The first function name will be fun_quadruple(int x)  The Second one will be fun_double (int x) 23
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  Predefined macros The followingmacro names are predefined in any translation unit: 26
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  28 Macros ==Text Replacement Predefinedmacros __VA_ARGS__ & # & ##
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  Conditional compilation Syntax: #ifdef,#endif, #if, #else, #ifndef Set of commands are included or excluded in source program before compilation with respect to the condition. 29
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  EXAMPLE PROGRAM FOR#IFDEF, #ELSE AND #ENDIF IN C:  “#ifdef” directive checks whether particular macro is defined or not. If it is defined, “If” clause statements are included in source file.  Otherwise, “else” clause statements are included in source file for compilation and execution. 30
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  EXAMPLE PROGRAM FOR#IFDEF, #ELSE AND #ENDIF IN C: 31
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  EXAMPLE PROGRAM FOR#IFDEF, #ELSE AND #ENDIF IN C: 32
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  EXAMPLE PROGRAM FOR#IFNDEF AND #ENDIF IN C:  #ifndef exactly acts as reverse as #ifdef directive. If particular macro is not defined, “If” clause statements are included in source file.  Otherwise, else clause statements are included in source file for compilation and execution. 33
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  EXAMPLE PROGRAM FOR#IFNDEF AND #ENDIF IN C: 34
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  EXAMPLE PROGRAM FOR#IFNDEF AND #ENDIF IN C: 35
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  EXAMPLE PROGRAM FOR#IF, #ELSE AND #ENDIF IN C: “If” clause statement is included in source file if given condition is true.  Otherwise, else clause statement is included in source file for compilation and execution. 36
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  Pragma directive inc  Pragma is implementation specific directive i.e each pragma directive has different implementation rule and use .  There are many type of pragma directive and varies from one compiler to another compiler .  If compiler does not recognize particular pragma the it simply ignore that pragma statement without showing any error message and execute the whole program assuming this pragma statement is not present. 38
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  Pragma directive in c 39
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  We will take #pragma startup  #pragma exit 40
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  What is #pragmastartup and #pragma exit in c programming language?  #pragma startup [priority]  #pragma exit [priority]  Where priority is optional integral number.  For user priority varies from 64 to 255  For c libraries priority varies from 0 to 63  Default priority is 100. 41
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  What is #pragmastartup and #pragma exit in c programming language?  pragma startup always execute the function before the main function pragma exit always execute the function after the main function.Function declaration of must be before startup and exit pragma directives and function must not take any argument and return void. If more than one startup directive then priority decides which will execute first.  startup:  Lower value: higher priority i.e. functions will execute first. If more than one exit directive then priority decides which will execute first.  exit:  Higher value: higher priority i.e. functions will execute first. For example 42
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  #pragma startup/exit ... is not supportedin gcc.  In gcc and clang, you should use __attribute__((constructor)) and __attribute__((destructor)) instead. 44
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  45 Quiz: Think howto write a code can be Removed or added to the Embedded C Program and Responsible on print Debug with Details
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  References 46  TheCase for Learning C as Your First Programming Language  A Tutorial on Data Representation  std::printf, std::fprintf, std::sprintf, std::snprintf…..  C Programming for Engineers, Dr. Mohamed Sobh  C programming expert.  fresh2refresh.com/c-programming  C programming Interview questions and answers  C – Preprocessor directives