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<UL>

	<LI><A HREF="#Heading1">- 27 -</A>

	<UL>

		<LI><A HREF="#Heading2">Programming in C</A>

		<UL>

			<LI><A HREF="#Heading3">NOTE</A>

			<LI><A HREF="#Heading4">What Is C?</A>

			<LI><A HREF="#Heading5">The GNU C Compiler</A>

			<UL>

				<LI><A HREF="#Heading6">Invoking GCC</A>

				<LI><A HREF="#Heading7">GCC Options</A>

			</UL>

			<LI><A HREF="#Heading8">NOTE</A>

			<UL>

				<LI><A HREF="#Heading9">Optimization Options</A>

				<LI><A HREF="#Heading10">Debugging and Profiling Options</A>

			</UL>

			<LI><A HREF="#Heading11">Debugging GCC Programs with gdb</A>

			<UL>

				<LI><A HREF="#Heading12">Compiling Code for Debugging</A>

				<LI><A HREF="#Heading13">gdb Basic Commands</A>

				<LI><A HREF="#Heading14">Sample gdb Session</A>

			</UL>

			<LI><A HREF="#Heading15">NOTE</A>

			<LI><A HREF="#Heading16">TIP</A>

			<LI><A HREF="#Heading17">NOTE</A>

			<LI><A HREF="#Heading18">Additional C Programming Tools</A>

			<UL>

				<LI><A HREF="#Heading19">xxgdb</A>

				<UL>

					<LI><A HREF="#Heading20">FIGURE 27.1.</A>

					<LI><A HREF="#Heading21">FIGURE 27.2.</A>

					<LI><A HREF="#Heading22">FIGURE 27.3.</A>

					<LI><A HREF="#Heading23">FIGURE 27.4.</A>

				</UL>

				<LI><A HREF="#Heading24">calls</A>

			</UL>

			<LI><A HREF="#Heading25">NOTE</A>

			<LI><A HREF="#Heading26">WARNING</A>

			<UL>

				<LI><A HREF="#Heading27">cproto</A>

			</UL>

			<LI><A HREF="#Heading28">NOTE</A>

			<LI><A HREF="#Heading29">WARNING</A>

			<UL>

				<LI><A HREF="#Heading30">indent</A>

				<LI><A HREF="#Heading31">gprof</A>

			</UL>

			<LI><A HREF="#Heading32">TIP</A>

			<UL>

				<LI><A HREF="#Heading33">f2c and p2c</A>

			</UL>

			<LI><A HREF="#Heading34">NOTE</A>

			<LI><A HREF="#Heading35">Summary</A>

			<LI><A HREF="#Heading36">TIP</A>

		</UL>

	</UL>

</UL>



<P>

<HR SIZE="4">



<H2 ALIGN="CENTER"><A NAME="Heading1<FONT COLOR="#000077">- 27 -</FONT></H2>

<H2 ALIGN="CENTER"><A NAME="Heading2<FONT COLOR="#000077">Programming in C</FONT></H2>

<P><I>by Rick McMullin</I></P>

<P>IN THIS CHAPTER</P>



<UL>

	<LI>What Is C?

	<P>

	<LI>The GNU C Compiler

	<P>

	<LI>Debugging GCC Programs with gdb

	<P>

	<LI>Additional C Programming Tools 501

</UL>



<P>Linux is distributed with a wide range of software-development tools. Many of

these tools support the development of C and C++ applications. This chapter describes

the tools that can be used to develop and debug C applications under Linux. It is

not intended to be a tutorial on the C programming language, but rather to describe

how to use the C compiler and some of the other C programming tools that are included

with Linux. In this chapter you will learn about the following:



<UL>

	<LI>What C is

	<P>

	<LI>The GNU C compiler

	<P>

	<LI>Debugging GCC applications with <TT>gdb</TT>

</UL>



<P>You also will look at some of the useful C tools that are included with the Linux

distribution. These tools include pretty print programs, additional debugging tools,

and automatic function prototypers.



<DL>

	<DT></DT>

</DL>





<DL>

	<DD>

<HR>

<A NAME="Heading3<FONT COLOR="#000077"><B>NOTE: </B></FONT>Pretty print programs

	are programs that automatically reformat code so that it has consistent indenting.

	

<HR>



</DL>



<H3 ALIGN="CENTER"><A NAME="Heading4<FONT COLOR="#000077">What Is C?</FONT></H3>

<P>C is a general-purpose programming language that has been around since the early

days of the UNIX operating system. It was originally created by Dennis Ritchie at

Bell Laboratories to aid in the development of UNIX. The first versions of UNIX were

written using assembly language and a language called B. C was developed to overcome

some of the shortcomings of B. Since that time, C has become one of the most widely

used computer languages in the world.</P>

<P>Why did C gain so much support in the programming world? Some of the reasons that

C is so commonly used include the following:



<UL>

	<LI>It is a very portable language. Almost any computer that you can think of has

	at least one C compiler available for it, and the language syntax and function libraries

	are standardized across platforms. This is a very attractive feature for developers.

	<P>

	<LI>Executable programs written in C are fast.

	<P>

	<LI>C is the system language with all versions of UNIX.

</UL>



<P>C has evolved quite a bit over the last 20 years. In the late 1980s, the American

National Standards Institute published a standard for the C language known as ANSI

C. This further helped to secure C's future by making it even more consistent between

platforms. The 1980s also saw an object-oriented extension to C called C++. C++ will

be described in the next chapter, &quot;Programming in C++.&quot;</P>

<P>The C compiler that is available for Linux is the GNU C compiler, abbreviated

GCC. This compiler was created under the Free Software Foundation's programming license

and is therefore freely distributable. You will find it on this book's companion

CD-ROM.

<H3 ALIGN="CENTER"><A NAME="Heading5<FONT COLOR="#000077">The GNU C Compiler</FONT></H3>

<P>The GNU C Compiler (GCC) that is packaged with the Slackware Linux distribution

is a fully functional, ANSI C compatible compiler. If you are familiar with a C compiler

on a different operating system or hardware platform, you will be able to learn GCC

very quickly. This section describes how to invoke GCC and introduces many of the

commonly used GCC compiler options.

<H4 ALIGN="CENTER"><A NAME="Heading6<FONT COLOR="#000077">Invoking GCC</FONT></H4>

<P>The GCC compiler is invoked by passing it a number of options and a number of

filenames. The basic syntax for invoking <TT>gcc</TT> is this:</P>

<PRE><FONT COLOR="#0066FF">gcc [options] [filenames]

</FONT></PRE>

<P>The operations specified by the command-line options will be performed on each

of the files that are specified on the command line. The next section describes the

options that you will use most often.

<H4 ALIGN="CENTER"><A NAME="Heading7<FONT COLOR="#000077">GCC Options</FONT></H4>

<P>There are more than 100 compiler options that can be passed to GCC. You will probably

never use many of these options, but you will use some of them on a regular basis.

Many of the GCC options consist of more than one character. For this reason you must

specify each option with its own hyphen, and you cannot group options after a single

hyphen as you can with most Linux commands. For example, the following two commands

are not the same:</P>

<PRE><FONT COLOR="#0066FF">gcc -p -g test.c

gcc -pg test.c

</FONT></PRE>

<P>The first command tells GCC to compile <TT>test.c</TT> with profile information

for the <TT>prof</TT> command and also to store debugging information within the

executable. The second command just tells GCC to compile <TT>test.c</TT> with profile

information for the <TT>gprof</TT> command.</P>

<P>When you compile a program using <TT>gcc</TT> without any command-line options,

it will create an executable file (assuming that the compile was successful) and

call it <TT>a.out</TT>. For example, the following command would create a file named

<TT>a.out</TT> in the current directory.</P>

<PRE><FONT COLOR="#0066FF">gcc test.c

</FONT></PRE>

<P>To specify a name other than <TT>a.out</TT> for the executable file, you can use

the <TT>-o</TT> compiler option. For example, to compile a C program file named <TT>count.c</TT>

into an executable file named <TT>count</TT>, you would type the following command.</P>

<PRE><FONT COLOR="#0066FF">gcc -o count count.c

</FONT></PRE>



<DL>

	<DT><FONT COLOR="#0066FF"></FONT></DT>

</DL>





<DL>

	<DD>

<HR>

<A NAME="Heading8<FONT COLOR="#000077"><B>NOTE:</B> </FONT>When you are using

	the <TT>-o</TT> option, the executable filename must occur directly after the <TT>-o</TT>

	on the command line. 

<HR>



</DL>



<P>There are also compiler options that allow you to specify how far you want the

compile to proceed. The <TT>-c</TT> option tells GCC to compile the code into object

code and to skip the assembly and linking stages of the compile. This option is used

quite often because it makes the compilation of multifile C programs faster and easier

to manage. Object code files that are created by GCC have a <TT>.o</TT> extension

by default.</P>

<P>The <TT>-S</TT> compiler option tells GCC to stop the compile after it has generated

the assembler files for the C code. Assembler files that are generated by GCC have

a <TT>.s</TT> extension by default. The <TT>-E</TT> option instructs the compiler

to perform only the preprocessing compiler stage on the input files. When this option

is used, the output from the preprocessor is sent to the standard output rather than

being stored in a file.

<H4 ALIGN="CENTER"><A NAME="Heading9<FONT COLOR="#000077">Optimization Options</FONT></H4>

<P>When you compile C code with GCC, it tries to compile the code in the least amount

of time and also tries to create compiled code that is easy to debug. Making the

code easy to debug means that the sequence of the compiled code is the same as the

sequence of the source code, and no code gets optimized out of the compile. There

are many options that you can use to tell GCC to create smaller, faster executable

programs at the cost of compile time and ease of debugging. Of these options the

two that you will typically use are the <TT>-O</TT> and the <TT>-O2</TT> options.</P>

<P>The <TT>-O</TT> option tells GCC to perform basic optimizations on the source

code. These optimizations will in most cases make the code run faster. The <TT>-O2</TT>

option tells GCC to make the code as fast and small as it can. The <TT>-O2</TT> option

will cause the compilation speed to be slower than it is when using the<TT> -O</TT>

option, but will typically result in code that executes more quickly.</P>

<P>In addition to the <TT>-O</TT> and <TT>-O2</TT> optimization options, there are

a number of lower-level options that can be used to make the code faster. These options

are very specific and should only be used if you fully understand the consequences

that using these options will have on the compiled code. For a detailed description

of these options, refer to the GCC manual page by typing <TT>man gcc</TT> on the

command line.

<H4 ALIGN="CENTER"><A NAME="Heading10<FONT COLOR="#000077">Debugging and Profiling

Options</FONT></H4>

<P>GCC supports several debugging and profiling options. Of these options, the two

that you are most likely to use are the <TT>-g</TT> option and the <TT>-pg</TT> option.</P>

<P>The <TT>-g</TT> option tells GCC to produce debugging information that the GNU

debugger (<TT>gdb</TT>) can use to help you to debug your program. GCC provides a

feature that many other C compilers do not have. With GCC you can use the <TT>-g</TT>

option in conjunction with the <TT>-O</TT> option (which generates optimized code).

This can be very useful if you are trying to debug code that is as close as possible

to what will exist in the final product. When you are using these two options together

you should be aware that some of the code that you have written will probably be

changed by GCC when it optimizes it. For more information on debugging your C programs,

refer to the &quot;Debugging GCC Programs with <TT>gdb</TT>&quot; section in this

chapter.</P>

<P>The <TT>-pg</TT> option tells GCC to add extra code to your program that will,

when executed, generate profile information that can be used by the <TT>gprof</TT>

program to display timing information about your program. For additional information

on <TT>gprof</TT>, refer to the &quot;<TT>gprof</TT>&quot; section in this chapter.

<H3 ALIGN="CENTER"><A NAME="Heading11<FONT COLOR="#000077">Debugging GCC Programs

with gdb</FONT></H3>

<P>Linux includes the GNU debugging program called <TT>gdb</TT>. <TT>gdb</TT> is

a very powerful debugger that can be used to debug C and C++ programs. It enables

you to see the internal structure or the memory that is being used by a program while

it is executing. Some of the functions that <TT>gdb</TT> provides for you are these:



<UL>

	<LI>It enables you to monitor the value of variables that are contained in your program.

	<P>

	<LI>It enables you to set breakpoints that will stop the program at a specific line

	of code.

	<P>

	<LI>It enables you to step through the code, line by line.

</UL>



<P>You can run <TT>gdb</TT> by typing <TT>gdb</TT> on the command line and pressing

Enter. If your system is configured properly, <TT>gdb</TT> should start and you will