C under Linux

Revised 21/10/2002
On the University central Linux servers the C/C++ compiler command is gcc
though for simple compilations you can use the command: c

To create a file for example 'hello.c'

     $ edit hello.c

(The Linux Pico Editor will be opened. Type the following in the editor.)

To compile the file 'hello.c'

     $ c hello.c

or use gcc with -o option

     $ gcc hello.c -o hello

To execute the file 'hello'

     $ run hello

This will output Hello World!...

Infact, there are two modes of program execution; these are interactive (the commands nice and run), and background (the & symbol and the command submit). Note that there are no cpu time limits or batch queues. To run an executable program you can simple type its name or use the run command. For example, you have compiled a C program into an executable program called myprog. The program can be executed with one of the following commands:

     $ myprog
     $ ./myprog

(if myprog exists elsewhere in the user's PATH then './' specifies that the file to be executed is in the present working directory)

     $ nice myprog     (please use this one or the next to be nice to other users)

For our c program 'hello.c'

     $ hello

     $ ./hello

Notes:

The source files must have the extension .c
The executable has no extension (it does NOT have the DOS or VMS extension .exe)
You can pass one extra compiler option by adding the option after the filename,
Full c/c++ compilation options (e.g. linking objects and libraries)
can be gained by using the gcc and g++ commands (try gcc --help or man gcc etc)

Using Library by C

Before starting, create the following files to be an example:

sub1.c , sub2.c , sub3.c and main.c

To compile and link these all four files at the same time:

     $ c main.c sub1.c sub2.c sub3.c

     $ gcc main.c sub1.c sub2.c sub3.c -o main

Then, the command

     $ run main

will output

      Sum is         5
      Mul is         6
      The biggest is 3

To create object of a file (compile without linking)

      $ gcc sub1.c -c    gives object file of sub1.c (that is sub1.o)
      $ gcc sub2.c -c    gives object file of sub2.c (that is sub2.o)
      $ gcc sub3.c -c    gives object file of sub3.c (that is sub3.o)

Creating Libraries (ar)
A library whose name is test of these functions can be created as follows:
```
       $ ar rcvf  libtest.a  sub1.o sub2.o sub3.o
      (see man ar)
```
You can add objects to the library with:
```
       $ ar rcvf libtest.a  sub4.o
```
To list the contents of the library:
```
       $ ar tv libtest.a
```
To list functions in a library:
```
       $ nm libtest.a
       (see man nm)
```
To delete an object from the library:
```
       $ ar dv libtest.a sub3.o
```
To link the library when compiling a C program main.c which requires sub1.o , sub2.o and sub3.o:
```
       $ gcc main.c -o main -L. -ltest
```
Note that lib and .a are dropped.The -L. options tells the linker that the library can be found in the current directory. If the library is not in the current directory then you should give the path:
$ gcc main.c -o main -L/home/yilmaz/C/lib -ltest
or
$ gcc main.c -o main -L$MYLIB -ltest
with
MYLIB=/home/yilmaz/C/lib

Note: Known problems when porting C programs from other platforms (e.g. ALPHA, Sun)

Math library math.h:
If you use math.h and you get compilation errors such as 'undefined reference to ...'
then you need to compile either with the -O2 option or the -lm option; or use the c command.
.... more problems (with solutions) will be included as they appear;
please report problems to me!

See also:

gcc_2.html
gcc.ps
gcc.ps.zip
http://www.gnu.org/software/gcc/gcc.html
http://gcc.gnu.org/onlinedocs/gcc-3.0/gcc.html
http://www.gnu.org/software/gcc/faq.html

system@gantep.edu.tr