2.1 Programs from Conception to Execution

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2.1 Programs from Conception to Execution

C++ programs are written in a high-level language using letters , numbers , and the other symbols you find on a computer keyboard. Computers actually execute a very low-level language called machine code (a series of numbers). So, before a program can be used, it must undergo several transformations.

Programs start out as an idea in a programmer's head. She writes down her thoughts in a file, called a source file or source code , using a text editor. This file is transformed by the compiler into an object file . Next a program called the linker takes the object file, combines it with predefined routines from a standard library, and produces an executable program (a set of machine-language instructions) . In the following sections, you'll see how these various forms of the program work together to produce the final program.

Figure 2-2 shows the steps that must be taken to transform a program written in a high-level language into an executable program.

Figure 2-2. Transformation of a high-level language into a program

Fortunately you don't have to run the compiler, assembler, and linker individually. Most C++ compilers use "wrapper" programs, which determine which tools need to be run and then run them.

Some programming systems go even further and provide the developer with an integrated development environment (IDE). The IDE contains an editor, compiler, linker, project manager, debugger, and more in one convenient package. Both Borland and Microsoft provide IDEs with their compilers.

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2.2 Creating a Real Program

Before you can actually start creating your own programs, you need to know how to use the basic programming tools. This section will take you step by step through the process of entering, compiling, and running a simple program.

This section describes how to use two different types of compilers. The first type is the standalone or command-line compiler. This type of compiler is operated from the command line. You type a command, and the compiler turns your source code into an executable program. The other type of compiler is contained in an IDE.

Most Unix systems use command-line compilers. A few IDE-type compilers are available for Unix, but they are rare. On the other hand, almost all the compilers used with Microsoft Windows are part of an IDE. For command-line die-hards, these IDEs contain command-line compilers as well.

2.2.1 Creating a Program Using a Command-Line Compiler

In this section you'll go through the step-by-step process needed to create a program using a command-line compiler. The program you're going to create will display the message "Hello World" on the screen. Instruction is given for using a generic Unix compiler, the Free Software Foundation's g++ compiler, Borland C++, and Microsoft Visual C++.

However, if you are using a Borland or Microsoft compiler, you might want to skip ahead to Section 2.2.2.

Note that, because compilers are continually being improved, the information in this section may not be accurate by the time you read it. As new compilers come out, we'll update this section and post the update on the O'Reilly web site at http://www.oreilly.com/catalog/cplus2.

2.2.1.1 Step 1: Create a place for your program

It is easier to manage things if you create a separate directory for each program you are working on. In this case you'll create a directory called hello to hold your hello program.

In Unix, type:

% mkdir hello
% cd hello

In MS-DOS, type:

C:> MKDIR HELLO
C:> CD HELLO

2.2.1.2 Step 2: Create the program

A program starts out as a text file. Example 2-1 shows the hello program in source form.

Example 2-1. Source for the hello.cpp program

#include <iostream>

int main(  )
{
    std::cout << "Hello World\n";
    return (0);
}

Use your favorite text editor to enter the program. Your file should be named hello.cpp .

Do not use a word-processing program such as Microsoft Word or WordPerfect to write your programs. Word-processing programs add formatting codes to files that confuse the compiler. You must use a text editor, such as the notepad program, that is capable of editing ASCII files.

2.2.1.3 Step 3: Run the compiler

The compiler changes the source file you just created into an executable program. Each compiler has a different command line. The commands for the most popular compilers are listed below.

2.2.1.3.1 Unix CC Compiler (Generic Unix)

Most Unix-based compilers follow the same generic standard. The C++ compiler is named CC. To compile your hello program, you need the following command:

%

CC -g -ohello hello.cpp

The -g option enables debugging. (The compiler adds extra information to the program to make it easier to debug.) The switch -ohello tells the compiler that the program is to be called hello , and the final hello.cpp is the name of the source file. See your compiler manual for details on all the possible options. There are several different C++ compilers for Unix, so your command line may be slightly different than is shown here.

2.2.1.3.2 Free Software Foundation's g++ Compiler

The Free Software Foundation, the GNU people, publishes a number of high-quality programs. (See the glossary entry "Free Software Foundation" for information on how to get their software.) Among their offerings is a C++ compiler called g++.

To compile the hello program using the g++ compiler, use the following command line:

%

g++ -g -Wall -ohello hello.cpp

The additional switch -Wall turns on all the warnings. When warnings are turned on, the compiler will warn you when it sees questionable code.

2.2.1.3.3 Borland's Turbo C++

Borland International makes a free Microsoft Windows C++ compiler called Borland-C++. This compiler is ideal for learning. The command line for Borland-C++ is:

C:>

bcc32 -v -N -w -tWC -ehello hello.cpp

The -v switch tells Borland-C++ to put debugging information in the program. Warnings are turned on by -w and stack checking by -N . The -tWC option tells Borland-C++ to output a "Console Application." That's a program that uses the standard C++ API (as opposed to the Windows API) and uses a MS-DOS console window for its input and output. Finally, -ehello tells Borland-C++ to create a program named hello, and hello.cpp is the name of the source file. See the Borland-C++ reference manual for a complete list of options.

2.2.1.3.4 Microsoft Visual C++ .NET

Microsoft Visual C++ .NET is another C++ compiler for Microsoft Windows. To compile the HELLO program, use the following command line:

C:>

cl /FeHELLO /GZ /RTCsuc /Zi /Wall hello.cpp

The /FeHELLO option tells the program to generate a program named HELLO.exe . Runtime checking is enabled by /GZ and /RTCsuc , and debugging is turned on with the /Zi option. All warning messages are enabled by /Wall . ^[1]

^[1] In the prerelease of Microsoft Visual Studio .NET, compilation with /Wall generated a large number of warnings caused by minor problems in Microsoft's own libraries. I expect these problems to be fixed in the production release of this code.

2.2.1.4 Step 4: Execute the program

Now, run the program by typing the following at the command prompt. (This works for both Unix and MS-DOS.)


hello

The message:

Hello World

will appear on the screen.

2.2.2 Creating a Program Using an Integrated Development Environment

The IDE provides a one-stop shop when it comes to programming. It take a compiler, editor, and debugger and wraps them into one neat package for the programmer. This package is presented inside a unified graphical interface that allows you to perform most program development operations with a few clicks of the mouse.

Since development environments tend to change, the particular version you use may operate slightly differently than is described in this chapter.

Each IDE is a little different, so we've included separate instructions for each one. (Note that compilers change much faster than books, so the information presented in these sections may be outdated . Check this book's page at the O'Reilly web site, http://www.oreilly.com/catalog/cplus2, for the latest information on compilation environments.)

2.2.2.1 Borland C++

Create a directory called HELLO to hold the files for our hello program. You can create a directory using the Windows desktop tools or by typing the following command at the MS-DOS prompt:
```
mkdir \HELLO
```
From Windows, double-click on the Borland C++ icon to start the IDE, or start the IDE using the "Start" menu. The program begins execution and displays a blank workspace, as shown in Figure 2-3.

Figure 2-3. Borland C++ initial screen
Select the File New item to create a project for our program. Select Console Wizard as shown in Figure 2-4 and click OK.

Figure 2-4. New Items selector
The Console Wizard dialog appears as shown in Figure 2-5. Select C++ for Source Type and click OK.

Figure 2-5. Project Options dialog box
The initial editing window appears as shown in Figure 2-6.

Figure 2-6. Initial editing window
Add your code to the file Unit1.cpp . The resulting code should look like:
```
#include <iostream>
int main(  )
{
    std::cout << "Hello World\n";
    return (0);
}
```
You can ignore the #pragma statements and comments that Borland-C++ has added. When you have finished, your screen will look like Figure 2-7.

Figure 2-7. Hello program
Compile and run the program by selecting the Debug Run menu item. The program will run and display "Hello World" in a window, as shown in Figure 2-8.

Figure 2-8. Hello program

2.2.2.2 Microsoft Visual C++

From Windows, start Microsoft Visual Studio .NET. A start screen will be displayed, as shown in Figure 2-9.

Figure 2-9. Microsoft Visual C++ initial screen
Click on File New Project to bring up the New Project dialog shown in Figure 2-10.

Figure 2-10. New Project dialog

In the Template pane, select "Manage C++ Empty Project." Fill in the Name field with hello . Change the Location field to the directory in which you wish to build the project. Click OK. The project screen now appears as shown in Figure 2-11.

Figure 2-11. Initial project screen
In the Solution Explorer tab, select Source Files. Now create the program using the File Add New Item menu. The Add New Item dialog appears as shown in Figure 2-12.

Figure 2-12. Add New Item dialog
Select C++ file as the file type and put hello.cpp in the name field. Click Done to bring up the editing window shown in Figure 2-13.

Figure 2-13. Editing window
Type the following lines into the hello.cpp window.
```
#include <iostream>
int main(  )
{
    std::cout << "Hello World\n";
    return (0);
}
```
Your results should look like Figure 2-14.

Figure 2-14. Completed program
Compile the program by selecting Build Build Hello. You may have to resize the windows to view the messages. If everything works, the screen should look something like Figure 2-15.

Figure 2-15. Result of the build
Run the program using the Debug Start Program without Debugging window menu item. An MS-DOS window appears and the program is run within it. The results are shown in Figure 2-16.

Figure 2-16. Sample run