Phase 1 consists of editing a file with an editor program, normally known simply as an editor (Fig. 1.6). You type a C++ program (typically referred to as source code) using the editor, make any necessary corrections and save the program on your computer’s disk. C++ source code filenames often end with the .cpp, .cxx, .cc or .C (uppercase) extensions which indicate that a file contains C++ source code. See the documentation for your C++ compiler for more information on filename extensions. Two editors widely used on Linux systems are vim and emacs. You can also use a simple text editor, such as Notepad in Windows, to write your C++ code.

Integrated development environments (IDEs) are available from many major software suppliers. IDEs provide tools that support the software development process, including editors for writing and editing programs and debuggers for locating logic errors—errors that cause programs to execute incorrectly. Popular IDEs include Microsoft^® Visual Studio 2015 Community Edition, NetBeans, Eclipse, Apple’s Xcode^®, CodeLite and Clion.

In Phase 2, you give the command to compile the program (Fig. 1.7). In a C++ system, a preprocessor program executes automatically before the compiler’s translation phase begins (so we call preprocessing Phase 2 and compiling Phase 3). The C++ preprocessor obeys commands called preprocessing directives, which indicate that certain manipulations are to be performed on the program before compilation. These manipulations usually include (i.e., copy into the program file) other text files to be compiled, and perform various text replacements. The most common preprocessing directives are discussed in the early chapters; a detailed discussion of preprocessor features appears in Appendix E, Preprocessor.

In Phase 3, the compiler translates the C++ program into machine-language code—also referred to as object code (Fig. 1.8).

Phase 4 is called linking. C++ programs typically contain references to functions and data defined elsewhere, such as in the standard libraries or in the private libraries of groups of programmers working on a particular project (Fig. 1.9). The object code produced by the C++ compiler typically contains “holes” due to these missing parts. A linker links the object code with the code for the missing functions to produce an executable program (with no missing pieces). If the program compiles and links correctly, an executable image is produced.

Phase 5 is called loading. Before a program can be executed, it must first be placed in memory (Fig. 1.10). This is done by the loader, which takes the executable image from disk and transfers it to memory. Additional components from shared libraries that support the program are also loaded.

Finally, the computer, under the control of its CPU, executes the program one instruction at a time (Fig. 1.11). Some modern computer architectures often execute several instructions in parallel.

Programs might not work on the first try. Each of the preceding phases can fail because of various errors that we’ll discuss throughout this book. For example, an executing program might try to divide by zero (an illegal operation for integer arithmetic in C++). This would cause the C++ program to display an error message. If this occurred, you’d have to return to the edit phase, make the necessary corrections and proceed through the remaining phases again to determine that the corrections fixed the problem(s). [Note: Most programs in C++ input or output data.] Certain C++ functions take their input from cin (the standard input stream; pronounced “see-in”), which is normally the keyboard, but cin can be redirected to another device. Data is often output to cout (the standard output stream; pronounced “see-out”), which is normally the computer screen, but cout can be redirected to another device. When we say that a program prints a result, we normally mean that the result is displayed on a screen. Data may be output to other devices, such as disks, hardcopy printers or even transmitted over the Internet. There is also a standard error stream referred to as cerr. The cerr stream (normally connected to the screen) is used for displaying error messages.