Compiling and Executing C Programs

COMPILING AND EXECUTING C PROGRAMS

C is a compiled language. So once a C program is written, you must run it through a C compiler that can create an executable file to be run by the computer. While the C program is human-readable, the executable file, on the other hand, is a machine-readable file available in an executable form.

The mechanical part of running a C program begins with one or more program source files, and ends with an executable file, which can be run on a computer.

The programming process starts with creating a source file that consists of the statements of the program written in C language. This source file usually contains ASCII characters and can be produced with a text editor, such as Windows notepad, or in an Integrated Design Environment. The source file is then processed by a special program called a compiler.

Note

Every programming language has its own compiler.

The compiler translates the source code into an object code. The object code contains the machine instructions for the CPU, and calls to the operating system API (Application Programming Interface).

However, even the object file is not an executable file. Therefore, in the next step, the object file is processed with another special program called a linker. While there is a different compiler for every individual language, the same linker is used for object files regardless of the original language in which the new program was written. The output of the linker is an executable or runnable file. The process is shown in Figure 2.4.

In C language programs, there are two kinds of source files. In addition to the main (.c) source file, which contains executable statements there are also header (.h) source files. Since all input and output in C programs is done through library functions, every C program therefore uses standard header files. These header files should be written as part of the source code for modular C programs.

The compilation process shown in Figure 2.5 is done in two steps. In the first step, the preprocessor program reads the source file as text, and produces another text file as output. Source code lines which begin with the # symbol are actually not written in C but in the preprocessor language. The output of the preprocessor is a text file

which does not contain any preprocessor statements. This file is ready to be processed by the compiler. The linker combines the object file with library routines (supplied with the compiler) to produce the final executable file.