Debugging is a methodical process of finding and fixing bugs in a computer program. **IMPORTANT NOTE:** This tag is ONLY for questions about debugging techniques or the process of debugging itself, NOT for requesting help debugging your code.
Debugging is a methodical process of finding and fixing bugs in a computer program or a piece of electronic hardware, thus making it behave as expected.
Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge in another. Many books have been written about debugging, as it involves numerous aspects, including interactive debugging, control flow, integration testing, log files, monitoring (application, system), memory dumps, profiling, Statistical Process Control, and special design tactics to improve detection while simplifying changes.
Four key techniques for debugging are syntax checking, adding comments, stepping and using breakpoints.
Syntax checking
Many good tools exist, including online-only tools, to check the syntax of your code. Checking the syntax means checking your code obeys the basic rules of the programming language or tool being used (e.g., missing end brackets, no end to an if statement). Syntax checking is done automatically in compiled languages (eg, C, C++, pascal) but not in interpreted or scripted languages (eg, javascript, perl, HTML). Some code editors include syntax highlighting or validation. Syntax checks can also be carried out for some data files or stylesheets, for example the JSON or CSS that your code uses.
Syntax checks will quickly help find spelling mistakes, missing or repeated statements, invalid expressions, and may also give warnings or suggested improvements. Syntax checkers are also known as linters, or code validators. Checking for valid syntax before running can identify errors quickly.
Stepping
Program stepping refers to using a tool to running your code line by line or a section at a time, examining the results including variables, the result of expressions, and the order that the program's steps are executed in. This is particularly useful in programs which do not give an error, or contain infinite loops.
Breakpoints
Breakpoints are particular places in your code in which you want to temporarily stop the code in order to check if it is running correctly so far, for example to check whether a value typed in was correctly stored in a variable you would add a breakpoint immediately after that line, then check the result. Using several different breakpoints allows you to very quickly find the area of the code which is causing the problem.
Breakpoints can be created using a debugging tool, or manually a very simple form of breakpoint could be adding a pop-up messages that waits for you to respond with OK, and can display a message containing program information (e.g., line number, function's name, values of variables).
Using comments
Adding comment to your code is good practice and allows you to describe the purpose of a short piece of code in human-readable form. Programming languages ignore all lines containing comments, but they can help you later to update your code or resolve problems if you add them as you first begin coding.
Applications and Tools for Debugging:
- WinDbg - A debugger for low-level debugging, mostly used for production debugging and difficult error solving.
- WinDbg also contains extensions for .Net debugging like ".Sos", ".SosEx" and more...
- OllyDbg - An assembly debugger mostly used for reverse engineering and cracking.
- Note that as for February 2014 OllyDbg only support 32 Bit application debugging.
- CSS online validator
- HTML online validator
- JSlint - javascript linter
- JSON online validator and formatter
Learning Sources:
Books:
Tutorials:
