A debugger is a computer program that is used to debug (and sometimes test or optimize) other programs.

When the program crashes, the debugger shows the position in the original code if it is a source-level debugger or symbolic debugger, commonly seen in integrated development environments. If it is a low-level debugger or a machine-language debugger it shows the line in the disassembly. (A "crash" happens when the program can't continue because of a programming bug . For example, perhaps the program tried to use an instruction not available on the current version of the CPU.)

Typically, debuggers also offer more sophisticated functions such as running a program step by step (single-stepping), stopping (breaking) (pausing the program to examine the current state) at some kind of event, and tracking the values of some variables. Some debuggers have the ability to modify the state of the program while it is running, rather than merely to observe it.

The same functionality which makes a debugger useful for eliminating accidental bugs allows it to be used as a cracking tool to learn how to evade copy prevention and other programmed limitations.

Debuggers make the debugging process much easier and faster, to the point where the availability of a good one for a particular language and platform can sway the decision to use that language rather than another language that is superior in other respects but lacks such tools.

An important difficulty is that software running under a debugger might behave differently than software running normally, because a debugger changes the internal timing of a software program. That makes it often very difficult to track down runtime problems in complex multi-threaded or distributed systems.

Some people find traditional debuggers hard to work with, and use instead a front-end.

Notable debuggers include:

• GNU Debugger (GDB)
• CodeView and the Visual Studio Debugger
• T-Bug , the integrated debugger in Perl 5
• AntiC
• Broadway
• DAEDALUS
• Java Platform Debugger Architecture
• adb
• sdb
• dbx
• Dynamic debugging technique (DDT), and its octal counterpart ODT
• Purify
• ladebug
• SoftICE
• Turbo Debugger
• TMON
• MacsBug
• Etnus TotalView
• Streamline Distributed Debugging Tool (DDT)
• Prism Parallel Debugger
• dgb_PHP_Debugger_and_Profiler client and server
• dgb_Library main
• doctorJ debugging the JavaDoc doccumentation with the code
• dprobes
• OllyDbg

See also

• Debugger_front-end
• Profiler_(computer_science)
• Computer programming
• Software testing
• Memory debugger
• Flaw detection
• Core dump

References

• Jonathan B. Rosenberg , How Debuggers Work: Algorithms, Data Structures, and Architecture, John Wiley & Sons, ISBN 0-471-14966-7