need help with conditional gdb debugging (of C code)

Question

I have a C code similar to:

int f() {
   for (int i = 0; i < 100; i++) {
   scanf flag;
   if(flag) 
      scanf data1;
   scanf data2;
   }
}

I want to break the execution only when flag == 0. How should I set the breakpoint (using gdb)?

Employed Russian · Accepted Answer · 2010-02-20 17:49:21Z

4

In the gdb console type

b (some_line) if flag == 0

EDIT:
If you can't print flag while stopped at some-line, then either:
- (A) your code is compiled with optimization (likely), or
- (B) you have a buggy compiler

If it's (A), add -O0 in addition to -g3.

If you can print flag, then you have a buggy version of GDB. Try upgrading to current 7.0.1 release.

edited Feb 20, 2010 at 17:49

Employed Russian

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answered Feb 20, 2010 at 9:58

kennytm

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5 Comments

Lazer Over a year ago

yes, i tried that already... I am getting Error in re-setting breakpoint 17: No symbol flag in current context.

anon Over a year ago

@dksjalk Have you compiled with debug information? gcc -g myfile.c

Potatoswatter Over a year ago

@dksjalk: or better — gcc -g3

Lazer Over a year ago

yes, I compiled with debug information (using Eclipse though), but I am not sure the debug info is there. Is there some way to check?

anon Over a year ago

@dksjalk The error you are getting is exactly the one you get if there is no debug info.

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