Compiling and running your own programs

Questions

• Which compilers are available and how do I run them?
• How can I set things up to run a specific version of java -- other than the default one?
• I've compiled my program successfully, but I get "command not found" when I try and run it. What's going on?
• The C compiler doesn't understand functions in the math library
• The C compiler doesn't understand socket() and other network functions.
• Why doesn't /usr/ucb/cc work under Solaris 2?
• What is a "bus error"?
• What is a "segmentation fault"?

Answers

• Which compilers are available and how do I run them?

  SUNPRO 4.0.1
          /opt/SUNWspro/bin/pc    Pascal compiler
          /opt/SUNWspro/bin/f77   Fortran compiler
          /opt/SUNWspro/bin/f90   Fortran90 compiler
          /opt/SUNWspro/bin/cc    C compiler
          /opt/SUNWspro/bin/CC    C++ compiler
   
  GNU
          /usr/local/gnu/bin/g++  C++ compiler
          /usr/local/gnu/bin/gcc  C compiler
   

  These two areas are in the default path, so you should not have to give full pathnames unless you have changed your default path.

  You can do this by typing
  

         set path = (/opt/SUNWspro/bin $path)
  

  ... you can add this to your .login if you wish; be sure you use the line as-written -- include the "$path".

• How can I set things up to run a specific version of java -- other than the default one?

  To learn how to set a specific version of java click here.

• The C compiler doesn't understand functions in the math library.

  You need to link with the math library. math.h only provides declarations for the math functions. You need to add "-lm" to the compiler command line to link with the math library, which contains the definitions:

  gcc -o foo foo.c -lm
  

• I've compiled my program successfully, but I get "command not found" when I try and run it. What's going on?

  The problem is that your home directory is not in your executable-search path. Your shell keeps a list of directories to search for executables. You can see this by typing
  

             echo $path
  

  
  to your unix prompt. If you want to run a program that's not in your path, you have to give a directory context for it, so the shell can find it. (If /usr/local/bin were not in your path, you'd have to type /usr/local/bin/emacs everytime you wanted to run emacs.)

  There are two fixes: 1) Use directory context - since the current directory is ".", you can run a program in the current directory by typing "./programname". For example, if your C program was "thing.c", and you compiled it with "cc -o thing thing.c", then you could run it with "./thing".
  2) Adjust your path - this one is a little more complicated, since how you do it depends on what shell you're using. This should work on just about every type:
  

             set path = ( $path . )
  

  
  Be very careful about typing that, since if you mess it up, you'll have to log out and log back in again to reset your path. Adventurous souls can add the above line to their .login, but I don't recommend it. Depending on what directory you cd to, having that as your path may give you odd behavior. I recommend "./programname"

  One more thing: using "test" as an executable name will drive you crazy. There is a system command called "test" -- it's generally for shell programming. If you name your compiled program "test", you will be unhappy. What happens is, if you forget to use "./test", and just type "test", the system will just give you a prompt back, as if your program had run, but generated no output. I know of a number of students who inserted numerous print statements into their code and recompiled over and over again, trying to figure out what was wrong, when what was wrong was they weren't running their program at all. The safest thing is to not name your program "test".

• The C compiler doesn't understand socket() and other network functions.

  This is similar to the math library above. Under Solaris 2, there are three different libraries that contain definitions for the networking functons. libsocket contains all of the socket related functions. libnsl contains general network service functions like getrpcent(). libresolv contains the resolver code. Here is an example of a program that uses all three:

  gcc -o foo foo.c -lsocket -lnsl -lresolv
  

• Why doesn't /usr/ucb/cc work under Solaris 2?

  This isn't a compiler, it's an ad for people to buy Sun's Berkeley compatability compiler, which doesn't work too well. You should use one of the other compilers available on the system.

• What is a "bus error"?

  Most modern processors require data to be aligned on certain boundaries (2, 4, or 8 bytes) for speed. Many of them will flag an attempt to access unaligned data as a bus error. This is usually caused by either dereferencing an uninitialized pointer, or trying to dereference something that is not a pointer. If your program generates a bus error, you should use a debugger to find out where it is and inspect pointer usage there.

• What is a "segmentation fault"?

  This is the error returned by the operating system when a program attempts to reference data outside of its valid virtual address space. The cause and solution are as for bus errors, above.