c_in_linux
TRANSCRIPT
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HowTo build simple C programs on Linux
1. Introduction
This document will step you though compiling and running simple C programs underthe Linux operating system. It is meant as a guide for beginners who may know how
to program in C but don't know how to build a C program on Linux. This documentuses simple C programs to illustrate how to build the programs under Linux. It
covers writing a basic C program but it is not meant as a guide to teach the
language. We will also step through the basics of writing a Makefile for your project.
This document also assumes that you know how to create/edit files on Linux and thatyou have the GNU C compiler installed. An easy way to tell if you have a C compiler
installed is by issuing the command 'which gcc'. We are also assuming that thecompile is executed from the command line. There are far too many GUI/IDE type
environments to cover otherwise.
2. A Simple program
2.1 Writing the source
The source of our first program is below:code:#include
main()
{
printf("Linuxquestions.org\n");
}
Save the program above and call it simplelq.c
Here is the breakdown of the program above.
The first line #include is a preprocessor directive. This basically tells thecompiler that we are using the functions that are in the stdio library. The stdio library
contains all the basic functions needed for basic input and output for our program.
The second line main() is a required function for every C program. main() is thestarting point for the program. Like all functions the body begins with a { (open curly
brace) and ends with a } (close curly brace).
The body of our main function printf ("Linuxquestions.org\n"); is a function
call to the printf function. printf stands for print formatted and has complex rules forprinting text, numbers to specific formats. Here we are just displaying the test
"Linuxquestions.org" to the screen. The \n at the end of string is a newline. It tellsprintf to end the line and start any additional text on the next line. All function calls
in C must end in a ;
2.2 Compiling the Source
The compile is done from the command line.code:
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$ gcc -o simplelq simplelq.c
$
gcc is the GNU C compiler. The -o option tells it what to name the output file and thesimplelq.c is the source file.
The output from the compiler will be a binary file called simplelq
2.3 Running the executable
In order to run our sample executable we will need to apply the execute permissionto the file. The we will execute it after.code:$ chmod 744 simplelq
$ ./simplelq
Linuxquestions.org
The output of our sample program produced the text "Linuxquestions.org" to theconsole (or screen). Try to add some more text to the sample program, recompileand watch the output.
3. Dealing w ith multiple sources
In most projects that are more that a couple functions you will most likely want to
split out the source into multiple files. Splitting the code allows the source to be
more manageable by avoiding huge source files and to group like functions together.Here is an example that has multiple sources:
3.1 The source filescode:/* File: appendall.h */
/* below is a forward deceleration of a function. It differs from a
function header by the semicolon at the end. Any source that wants to
use the appendall function needs to include this header file. */
void appendall( int iArgCount,
char * iArgs[],
char * szReturnBuffer,
int iSize );
code:/* File: appendall.c */
#include
void appendall( int iArgCount,
char * iArgs[],
char * szReturnBuffer,
int iSize )
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{
int i = 0;
for ( i = 0; i < iArgCount; i++ ) /* Loop through all the arguments
*/
{
/* Test to see if the added length of the new arg will exceed */
/* the length of our buffer */
if (( strlen( szReturnBuffer ) + strlen( iArgs[i] )) < iSize )
{
strcat( szReturnBuffer, iArgs[i] ); /* concatenate */
strcat( szReturnBuffer, " " ); /* add a string */
}
else
{
printf( "Error: exceeded buffer size\n");
break;
}
}
}
code:/* File appendallmain.cpp */
*/ This include will pull in the function declaration for appendall.h
*/
#include "appendall.h"
#define SIZE 500
main( int argc, char * argv[])
{
char szNewString[SIZE]; /* declare a character array of size 500 */
appendall( argc, argv, szNewString, SIZE ); /* Call the function */
printf("%s", szNewString );
}
3.2 Compiling the Source
The compile is done from the command line.
There are a couple ways to do this. One is to compile and link in one step and the
other is to build the objects separately and then link.
Compile and link multiple sources in one step.code:$ gcc -o appendall appendall.c appendallmain.c
$
Compile and link in multiple steps:code:
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$ gcc -c appendall.c
$ gcc -c appendallmain.c
$ gcc -o appendall appendall.o appendallmain.o
$
The -c flag tells the compiler to compiler only and not call the linker.
It is easier to build and link in one step, but if you are using Makefiles to manageyour project the separate compile and link makes building much quicker.
Here is a simple Makefile for building the above sources:code:all: appendall
appendall.o: appendall.c appendall.h
gcc -c appendall.c
appendallmain.o: appendallmain.c appendall.h
gcc -c appendallmain.c
appendall: appendall.o appendallmain.ogcc -o appendall appendall.o appendallmain.o
clean:
rm *.o appendall
Run ake to build the sources:mcode:$ make
gcc -c appendall.c
gcc -c appendallmain.c
gcc -o appendall appendall.o appendallmain.o
$
Here is the basic breakup of a Makefile rule:
target ... : prerequisites ...command......
There must be a character before all the commands after a rule. Spaces
instead of tabs will result in errors.
4. Suggest Links
http://www.gnu.org/software/gcc/gcc.htmlhttp://www.gnu.org/manual/make/html...r/make_toc.html
http://www.linuxquestions.org/questions/search.php?s=