Third FAQ

for

Project 2 -- fork, exec, and wait

Q. We tried running gimp in the EL building on Sun workstation but for some reason, it gave us a "FATAL" error message. Is there a certain syntax to invoke GIMP?

A. There is no special syntax to invoking gimp. To invoke gimp from a command line, you can just type: 

% gimp
To invoke gimp on a particular file from a command line, you can just type: 
% gimp file1
(or whatever the name of the file is that you want to edit with gimp).

Similarly, you can just invoke gimp from within your code using exec, just as you would with any other program.

If you could be more specific about what the error message said and under what circumstances it happened, I could give a more specific answer to what your problem is.

Q. I have a question regarding gimp? Each time I execute gimp, I get this message on the bash screen

"ld.so.1: /usr/local/lib/gimp/1.0/plug-ins/aa:  fatal: libaa.so.1: open
failed:  No such file or directory
wire_read: unexpected EOF(plug-in crashed?)"

However, even when this message appears, the gimp program does load and execute. For the create a new picture part it works fine except for the same message pops up each time I run the gimp part. I don't know how to correct this problem? And since the gimp still executes even with this message, is this something to worry about?

A. This is an error with the gimp installation on some of the machines. It means that some of the functionality will probably be missing from gimp when the user runs it. (It is probably right that a plug-in crashed -- whatever functionality was provided by that plug-in won't be there.)

Don't worry about this problem for your second project -- it isn't caused by your code or set-up. As long as you get gimp running well enough to do some editing of files, that is enough.

However, when you have problems like this on the system, you should report them to Jim Summers (send email to jsummers or jsummers@cs.ou.edu), so that he can find out about them and fix them.

Q. As our group memebers are working on the project we got stuff where it says on the project "...if PIC_EDIT isn't set, gimp" what does this exactly mean. Do we need to set PIC_EDIT using putenv(const char*) and also how are we supposed to invoke a piceditor, is there a particular function for that? We have been working on this for several hours, but could not figure out.

A. Your program (PicShare) should not set the PIC_EDIT environment variable. Instead, your program should check to see if PIC_EDIT has already been set in its environment. There are two basic possibilities. One is that PIC_EDIT has been set, the other is that it hasn't. If PIC_EDIT has been set, your program should try to use whatever value PIC_EDIT has been set to. So, if PIC_EDIT has been set to gimp then your program should try to run gimp, if PIC_EDIT has been set to xv then your program should try to run xv, if PIC_EDIT has been set to xpaint then then your program should try to run xpaint, if PIC_EDIT has been set to asLKUGkjb2 then then your program should try to run asLKUGkjb2. (Note that your program will fail to run some of these programs, because they are not installed on the system, because they are not actual programs, or because the user doesn't have the program in his or her path, etc. This is fine. Your program should TRY to use the value in PIC_EDIT. If PIC_EDIT is set to a value of a real program that is installed on the system in the users path, etc., then your program should succeed in running PIC_EDIT. Otherwise, it is fine for your program to fail.)

If PIC_EDIT has not been set, your program should use gimp. (Again, if gimp is installed on the system in the users path, etc., then your program should succeed in running gimp. Otherwise, it is fine for your program to fail.)

All of this means two things. One is that your program will want to check the value of the variable PIC_EDIT in its environment. Two is that in order to test your program, you will want to try setting the value of PIC_EDIT outside your program, then running your program. We have discussed in class (and the textbook also talks about) ways to do these things.

As for invoking a picture editor, there is no special function to do this, but there are family of system calls, any of which can be used to invoke another program -- exec.

Q. Im not quite sure how to copy blank.jpg to the file that the user wants to create....does it have anything to do with the open(...) call discussed in class?

A. You can copy the file any way you want. You can use the POSIX I/O system calls that we just covered, the ANSI C Standard I/O routines that we covered near the beginning of the semester, or you could have your program fork off a child that executes the cp command.

Q. Can you give me a hint on copying blank.jpg to the user specified jpg file? The "cp" command did not work inside code, but it worked as a shell command. Why is this?

A. The cp command worked fine for me inside code. If you are constructing filenames using the C string functions, perhaps you aren't using them correctly. Please see the second FAQ for this assignment.