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but we left the <literal>i=5;</literal> line out. As we did not initialize <symbol>i</symbol>, it had whatever number happened to be in that area of memory when the program ran, which in this case happened to be <literal>4231</literal>.
The <command>gdb</command> command displays the stack frame every time we go into or out of a function, even if we are using <command>up</command> and <command>down</command> to move around the call stack. This shows the name of the function and the values of its arguments, which helps us keep track of where we are and what is going on. (The stack is a storage area where the program stores information about the arguments passed to functions and where to go when it returns from a function call.)
Examining a Core File with gdb
To examine a core file, start up <command>gdb</command> in the usual way. Instead of typing <command>break</command> or <command>run</command>, type
(gdb) <userinput>core <replaceable>progname</replaceable>.core</userinput>
If the core file is not in the current directory, type <userinput>dir /path/to/core/file</userinput> first.
The debugger should display something like this:
<prompt>%</prompt> <userinput>gdb <filename><replaceable>progname</replaceable></filename></userinput>
GDB is free software and you are welcome to distribute copies of it
under certain conditions; type "show copying" to see the conditions.
There is absolutely no warranty for GDB; type "show warranty" for details.
GDB 4.13 (i386-unknown-freebsd), Copyright 1994 Free Software Foundation, Inc.
(gdb) <userinput>core <filename><replaceable>progname</replaceable>.core</filename></userinput>
Core was generated by `<filename><replaceable>progname</replaceable></filename>'.
Program terminated with signal 11, Segmentation fault.
Cannot access memory at address 0x7020796d.
#0 0x164a in bazz (anint=0x5) at temp.c:17
(gdb)
In this case, the program was called <filename><replaceable>progname</replaceable></filename>, so the core file is called <filename><replaceable>progname</replaceable>.core</filename>. We can see that the program crashed due to trying to access an area in memory that was not available to it in a function called <function>bazz</function>.
Sometimes it is useful to be able to see how a function was called, as the problem could have occurred a long way up the call stack in a complex program. <command>bt</command> causes <command>gdb</command> to print out a back-trace of the call stack:
(gdb) <userinput>bt</userinput>
#0 0x164a in bazz (anint=0x5) at temp.c:17
#1 0xefbfd888 in end ()
#2 0x162c in main () at temp.c:11
(gdb)

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