---

Writing, compiling and running C++ programs

---

• C/C++ Programming
  • Java was designed after C++

    The designer of Java thought that C++ has too many features and designed a "stripped down" version of C++

    (In that spirit, Microsoft's C# is also a "stripped down" language of C++. They first wanted to call the new language C--...)

    ---

  • Knowing Java will help understand C++, but it may also make it complicated - because the same construct in C++ has a different meaning than in Java

  ---

  ---

  ---

• C++ program
  • A C/C++ program consists of one or more functions

    ---

  • There are two kinds of functions in C++:

    Member functions Stand-alone functions

    ---

    ---

  • A member function is contained inside a class definition:

    class ClassName { void function1() // A member function { .... } }

    A member function in C++ always has an implicit parameter - and it is similar to a member function in Java

    ---

  • A stand-alone function is not contained inside any class definition:

    void function2() // A stand-alone function { .... }

    A stand-alone function in C++ done not have an implicit parameter - and it is similar to a class function in Java

  ---

  ---

• The main (stand-alone) function
  • The execution of a C++ program begins with the main() stand-alone function

  • Therefore, a C/C++ program must contain the function:

    int main(int argc, char *argv[]) { ... }

    (I will not explain the strange char * notation now... see pointer variables)

    ---

  • A C/C++ program begins its execution at the function main(argc, argv)

    The main function will usually call (invoke) other (stand-alone or member) functions during the program execution.

  ---

  ---

• The classic first C/C++ program
  • Example C++ program:

    #include <iostream.h> // Header file containing useful definitions... int main(int argc, char *argv[]) { cout << "Hello World\n"; }

    ---

  • Example Program: (Demo First C++ program)                                                
    • Program file: click here

  ---

• How to compile and run a single file C++ program
  • CC is the UNIX command used to compile C++ programs

  • The general command syntax for CC is:

    CC [options] ProgramFileName.C

  • The program file name MUST end in ".C" or ".cc"

  • The output of the compiler is a computer executable program a.out

  • To run the program, you type at the UNIX prompt:

    a.out

  ---

  ---

• Commonly used (most useful) compiler options

  Option	Meaning	Example	What does it do
  -o FileName	Rename the executable output file	CC -o myProg myProg.C	Compiler will rename executable output file from a.out to myProg
  -g	Debug Mode	CC -g myProg.C	Compiler will insert additional information in output a.out that can be use with a debugger (a tool to help programmers find errors in the program)
  -c	Create relocatable object code	CC -c myProg.C	Compiler will NOT produce a directly executable computer program, but a program that can be combined with other "relocatable" codes NOTE: use this option when your program consists of multiple text files
  -lLibFile	Specify an additional library file	CC myProg.C -lmath	Tell the C++ compiler to "link in" (include) functions from the "math" function library. The actual UNIX filename for a C++ library file "math" is "libmath.a"

  • Many of these options can be combined.

  • Examples:

    CC -o myProg myProg.C	Compile myProg.C into the executable output file myProg (instead of a.out
    CC -g -c myProg.C	Produce relocatable object code with debug information

    ---

  • Concrete example:

    The Hello World program can also be compiled and run as follows:

    Compile: CC -o Hello Hello.C Run: Hello

    The -o option will rename the output file a.out to Hello

  ---

  ---

• Compiling C/C++ programs that consist of multiple files

  • Suppose your C/C++ program consists of multiple files, e.g.: myFile1.C and myFile1.C.

  • The commands you need to produce the program called myProg are:

    CC -g -c myFile1.C // This command will produce the // relocatable object file myFile1.o // (which can be combined with other // relocatable object files CC -g -c myFile2.C // This command will produce another // relocatable object file myFile2.o // // We can now combine these files ! CC -o myProg myFile1.o myFile2.o // Make runnable program named "myProg" // from myFile1.o and myFile2.o

    ---

  • NOTE: Use the -g option when you are developing your C/C++ program

    When it crashes, you can use the debugger to track down the errors.

    Once you have tested your program thoroughly and made sure that it works, then recompile ALL the program files again, but WITHOUT the -g option:

    CC -fast -c myFile1.C (optimize code to run fast) CC -fast -c myFile2.C CC -o myProg myFile1.o myFile2.o

  ---

  ---

• C/C++ Pre-processor
  • Before a C/C++ program is compiled, the text of the C/C++ program is first pre-precessed by the C/C++ preprocessor (this is another program that is automatically run when you type "CC" to compile a C/C++ program)

  • The most commonly used C/C++ Pre-processor # directives:

    #define SYMBOL VALUE (Defines a symbolic constant) #include <FILENAME> (Insert file FILENAME in this spot) #include "FILENAME" (Insert file FILENAME in this spot)

    The brackets < ... > indicates that the inserted file is found in C++'s include directory

    The quotes " ... " indicates that the inserted file is found in the current directory

    ---

  • Always include the C++ standard "header" file in every C++ program:

    #include <iostream.h>

    This header file contains commonly used constants and variables.

  ---

  ---

• #define
  • The #define directive defines symbolic value

    Example:

    #define ABC abcdefghijk #define XYZ "Hello World !" int main(int argc, char *argv[]) { ABC XYZ ABC abc }

    The C pre-processor will replace each ABC with abcdefghijk

    ---

  • NOTE:

    The symbolic name is case sensitive

    ---

  • Example Program: (Demo above code)                                                
    • Prog file: click here

    To see the effect of #define, do the following:

    CC -P define.C Use an editor and look in the file define.i

  • NOTE: if a symbol SYMBOL has already been defined previously, you must use #undef SYMBOL to undefine it before assigning it with a different value !

  ---

  ---

• #include: file inclusion mechanism of C/C++ pre-processor
  • The #include directive will replace the include file name with the content of the file

    Example:

    #include "define.C" ================================== #include "define.C"

    The line #include "define.C" is replaced by the content of the file

    ---

  • Example Program: (Demo above code)                                                
    • Prog file: click here

  • To see the effect of #include, do the following:

    CC -P include.C Use an editor and look in the file include.i

    ---

  • NOTE:
    • #include "FILENAME" will look for the include file in the current working directory

    • #include <FILENAME> will look for the include file in the system directories /usr/include/* and the directory paths specified using the -I (include) option

    ---

  • NOTE: #include can be NESTED
    • Example Program: (Demo NESTED #include) --- click here          

    • To see the effect of #include, do the following:
      • CC -P NestedInclude.C
      • Use an editor and look in the file NestedInclude.i

  ---