Friday, September 29, 2006

Linux unix beginners with c programming

I hope this helps out. Let¡¦s start out with the basics.


Source: Youve probably seen this before Download Source In Linux (or unix) you will most likely be dealing with source code. This is actually the raw instructions that are written by the programmer. You can not run these! So dont try icon_smile.gif. You need to first compile them (well get to that later)

Binaries: Binaries are code that has been compiled. If you are downloading binaries you will need to insure that the binary was compiled on the same distro and chipset you are using. Most Linux users will always say it is better to compile everything from the source. In most cases this is true. But, if you are a beginner try to find binaries:-)

Compiler: This is the actual program that interprets the source into a binary format. Logically, your compiler must be for the language the source was written. The vast majority of the time it will be a C compiler, the most common is gcc.

Files you will need:
A compiler (duh) ok for this tutorial we are going to use gcc.

Redhat 8.0



Some more basics:

Another thing a lot of beginners get confused with is the difference between a script and the source for a program. Scripts like pearl, PHP, ASP, and VBScript are interpreted at runtime. A compiled program is interpreted when you actually compile it, and then simply run. This means respective to their complexity compiled programs run faster than scripts.

Most software for Linux and other open source platforms are distributed as source code, usually a compressed archive commonly known as the tarball. This just means the file is in a compressed format, pretty much the same thing as a ZIP file.

Usually before you compile any programs, you should be logged in is a root user. You can do this by logging in as root or by typing su at the command line.

Another common mistake people make is to not have the required libraries. Libraries are shared code, that a program needs to run. For example: most programs that use extensive references to a certain type of protocol, such as SNMP will use a common library written by another programmer. Always check the readme file to see what libraries a program might need.

OK, the start out with a simple program we could write:

Int main(){
Printf(¡§Hello, world¡¨);

All this program does, is print hello world, easy enough, let's save it as test.c. Now to compile it just type:

gcc test.c

Now we should have a working binary program called a.out by default. If you want to give it a different name just type:

gcc test.c --o test1

The will output the file as test1.

Now remember how we talked about libraries, well libraries are included in source by the following:


All includes will be displayed at the top of the source code to be within good programming principles. Now, when we compile our program that contains includes we need to tell GCC where the library is located, so that a permanent link can be made within the program. We do this by the following:

gcc test.c --o test1 --L/usr/lib --ISDL

OK, here's quick English rundown of what we just did. We told GCC to compile our source test.c and output it as test1 and told it that the library SDL was located in /usr/Lib.

Now I hope this helped you guys out a little bit. The final thing I'm going to cover, is a lot of people see in the install files of a lot of programs that they need to run ./configure. Now when I was just beginning I used to get frustrated, because I would type that at the command line, and I would get file not found. The trouble you're having is you are not in the correct shell of Linux. To fix this just type:

sh ./configure

OK, that just about wraps it up.

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