HP gnu source-level debugger 5992-4701 manual Stopping and Continuing, Breakpoints

5 Stopping and Continuing

The principal purpose of a debugger is to let you stop your program before it terminates abnormally or runs into trouble, so that you can investigate and determine the reason.

Inside GDB, your program can stop for several reasons, such as a signal, a breakpoint, or reaching a new line after a GDB command such as step. You can then examine and change variables, set new breakpoints or remove old ones, and then continue execution. Usually, the messages shown by GDB provide information on the status of your program―but you can also explicitly request this information at any time.

info program Display information about the status of your program: whether it is running or not, what process it is, and why it stopped.

5.1 Breakpoints

A breakpoint makes your program stop whenever a certain point in the program is reached. For each breakpoint, you can add conditions to control in finer detail whether your program stops. You can set breakpoints with the break command and its variants. (see “Setting breakpoints” (page 52)) You can stop your program by line number, function name or an address in the program.

You can arrange to have values from your program displayed automatically whenever GDB stops at a breakpoint. See “Automatic display” (page 89).

In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set breakpoints in shared libraries before the executable is run. See “Debugging support for shared libraries” (page 210).

A catchpoint is another special breakpoint that stops your program when a certain kind of event occurs, such as the throwing of a C++ exception or the loading of a library. As with watchpoints, you use a different command to set a catchpoint (see “Setting catchpoints” (page 56)), but apart from that, you can manage a catchpoint like any other breakpoint. (To stop when your program receives a signal, use the handle command; see “Signals” (page 67).)

GDB assigns a number to each breakpoint, watchpoint, or catchpoint when you create it; these numbers are successive integers starting with one. In many of the commands for controlling various features of breakpoints you use the breakpoint number to say which breakpoint you want to change. Each breakpoint may be enabled or disabled; if disabled, it has no effect on your program until you enable it again.

Some GDB commands accept a range of breakpoints on which to operate. A breakpoint range is either a single breakpoint number, like '5', or two such numbers, in increasing order, separated by a hyphen, like '5-7'. When a breakpoint range is given to a command, all breakpoint in that range are operated on.

5.1 Breakpoints 51