Programming in C

404 Chapter 18 Debugging Programs

i = 3

(gdb) break foo Put a breakpoint at the start of foo

Breakpoint 2 at 0x1c98: file p18-5.c, line 13.

(gdb) continue Continue execution

Continuing.

Breakpoint 2, foo (x={month = 10, day = 11, year = 2004}) at p18-5.c:13

13 ++x.day; 0x8e in foo:25: {

(gdb) print today Display value of today

No symbol "today" in current context

(gdb) print main::today Display value of today from main

$11 = {

month = 10,

day = 11,

year = 2004

}

(gdb) step

15 return x;

(gdb) print x.day

$12 = 12

(gdb) continue

Continuing.

Program exited normally.

(gdb)

Note one feature of gdb: After a breakpoint is reached or after single stepping, it lists the

line that will be executed next when you resume execution of your program, and not

the last executed line.That’s why arraywas still not initialized the first time it was dis-

played. Single stepping one line caused it to be initialized. Also note that declarations that

initialize automatic variables are considered executable lines (they actually do cause the

compiler to produce executable code).

Listing and Deleting Breakpoints

Once set, breakpoints remain in a program until gdbexits or until you delete them.You

can see all the breakpoints that you have set by using the info breakcommand, as

follows:

(gdb) info break

Num Type Disp Enb Address What

1 breakpoint keep y 0x00001c9c in main at p18-5.c:20

2 breakpoint keep y 0x00001c4c in foo at p18-5.c:13

Program 18.5 Continued