I have an array that I am constantly modifying. After my program is finished executing my modifications don't quite do what I want them to do, so my array doesn't turn out the way that I want. I have a function that reads the contents of the array. Is there a way to use gdb and place a breakpoint somewhere, then run my function that reads the content of the array? I want to find out where the problem occurs. Gdb does not let me run "p readArray()". f I have a breakpoint.
3 Answers
Use "commands" to run a command whenever you hit a particular breakpoint. For example, to run the command on the first breakpoint:
(gdb) commands 1 Type commands for when breakpoint 1 is hit, one per line. End with a line saying just "end". > call readArray() > end
You can use "info break" to determine the number of the breakpoint you are interested in.
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Clifford
Your GDB fu is obviously better than mine. My suggested "dirty" solution works in debuggers that do not have the ability to call arbitrary functions, but I guess that's irrelevant in this case.
Set the breakboint at address. Get the address of your array at a point where you malloc or statically create array and set the breakpoint at address.
break *addr "set breakpoint at address addr"
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A 'dirty' method is to modify the program-counter register to the address of a location in your code where the display function is called. Be sure to set a break-point after the call so that you can restore the program-counter to its original value if you want the code to continue correctly thereafter.
Even dirtier, if the function does not take parameters, is to set the program-counter to the address of the first instruction in the function. In this case place a break-point at the return statement and restore the program-counter there, otherwise the return will return to the caller of the function of the first break-point which may not be what you would want.
That said, the debugger is perfectly capable of displaying array contents via a "watch", so unless the content requires specific interpretation to make sense of it, that would surely be a better method?
Another non-debugger work-around would be to have the array implemented as a memory mapped file or shared memory, then use a separate process to map and display the same file or memory. This technique would be OS specific.
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