Hi, friends:

I'm trying to use GNU gdb to detect a floating exception in my code. That exception occurs only when my time step is 2520 and iteration step is 3. So I have to wait a very long time(one day) to reach that exception point. Seems there is a trick called "conditional breakpoint" in gdb. Below is a brief fram of my code:

c-------------------------

c program my_prog

1 do it=1, it_max

2 do iter=1,iter_max

3

4 some tri-diagonal solver stuff

5

6 some convergence creterion

7 enddo

8 enddo

9 end

c-------------------------

I launch the gdb, and run the program, then I want to use the following GDB command to put a conditional breakpoint on line 1:

//--------

break 1 if it.ge.2520

//--------

it gives me back an error message saying:

//----

No symbol "it" in current context.

//----

Seems that the gdb doesn't recognize the variable "it" for me. What's the metter? I looked into some manu of gdb, saying that it's because "it" is out of the scope of something, but I don't quite understand and don't know how to get through.

Thank you very much if you can give me a hand.

wen long

You are likely to get a much better response posting this to a gnu/gcc/cc/... newsgroup.

I do not use gdb (i.e. I do not know if your command syntax/semantics is OK) but your code looks like Fortran and the added line some C/Fortran hybrid?

If you have not built a symbol table then the debugger will not be able to do much when you refer to "it". A symbol table is not usually built by default. Have you passed the "-g" flag when you compiled?

I would suggest better options for understanding your problems are:

(a) read the core file to find where and why the exception occurred. This is usually sufficient to find the odd underflow/overflow/divide_by_zero exceptions.

(b) add exception handlers (routines to be called when an exception occurs). This is the most flexible solution enabling you to do pretty much whatever you want.

Dear Andy:

Thanks for your reply. I did use -g option to enable the gdb. My code is purely Fortran, not easy to hook some exception handler onto it. There is a core file generated, but I don't know how to open it. Can you give more directions? Thanks again,

Wen

>> My code is purely Fortran, not easy to hook some exception handler onto it.

On the unix workstations that I have used it has always been very easy to add exception handlers to Fortran code. A quick google is a bit negative for g77 though:

http://www.delorie.com/gnu/docs/g77/g77_630.html

It looks doable but messy.

>> There is a core file generated, but I don't know how to open it. Can you give more directions?

"man gdb" says the command is "gdb -c core"

Andy, Thanks a lot. Now I got the basic idea. The gdb I'm using doesn't support variables stored in common blocks or EQUIVALENCE. While I'm using many many common blocks.

That's why when I use "p it", it doesn't show me the value of variable "it" since it's in a common block.

Wen