GDB: break if variable equal value

Question

I like to make GDB set a break point when a variable equal some value I set, I tried this example:

#include <stdio.h>
main()
{ 
     int i = 0;
     for(i=0;i<7;++i)
        printf("%d\n", i);

     return 0;
}

Output from GDB:

(gdb) break if ((int)i == 5)
No default breakpoint address now.
(gdb) run
Starting program: /home/SIFE/run 
0
1
2
3
4
5
6

Program exited normally.
(gdb)

Like you see, GDB didn't make any break point, is this possible with GDB?

Answer 1

in addition to a watchpoint nested inside a breakpoint you can also set a single breakpoint on the 'filename:line_number' and use a condition. I find it sometimes easier.

(gdb) break iter.c:6 if i == 5
Breakpoint 2 at 0x4004dc: file iter.c, line 6.
(gdb) c
Continuing.
0
1
2
3
4

Breakpoint 2, main () at iter.c:6
6           printf("%d\n", i);

If like me you get tired of line numbers changing, you can add a label then set the breakpoint on the label like so:

#include <stdio.h>
main()
{ 
     int i = 0;
     for(i=0;i<7;++i) {
       looping:
        printf("%d\n", i);
     }
     return 0;
}

(gdb) break main:looping if i == 5