debugging interview questions
Top debugging frequently asked interview questions
I find programming in PHP quite frustrating. Quite often I will try and run the script and just get a blank screen back. No error message, just empty screen. The cause might have been a simple syntax error (wrong bracket, missing semicolon), or a failed function call, or something else entirely.
It is very difficult to figure out what went wrong. I end up commenting out code, entering "echo" statements everywhere, etc. trying to narrow down the problem. But there surely must be a better way, right?.
So, is there a way to get PHP to produce useful error message like Java does?
Can anyone recommend good PHP debugging tips, tools and techniques?
Source: (StackOverflow)
How do I debug a Node.js server application?
Right now I'm mostly using alert debugging with print statements like this:
sys.puts(sys.inspect(someVariable));
There must be a better way to debug. I know that Google Chrome has a command-line debugger. Is this debugger available for Node.js as well?
Source: (StackOverflow)
What is this?
This is a number of answers about warnings, errors and notices you might encounter while programming PHP and have no clue how to fix. This is also a Community Wiki, so everyone is invited to participate in adding to and maintaining this list.
Why is this?
Questions like "Headers already sent" or "Calling a member of a non-object" pop up frequently on Stack Overflow. The root cause of those questions is always the same. So the answers to those questions typically repeat them and then show the OP which line to change in his/her particular case. These answers do not add any value to the site because they only apply to the OP's particular code. Other users having the same error can not easily read the solution out of it because they are too localized. That is sad, because once you understood the root cause, fixing the error is trivial. Hence, this list tries to explain the solution in a general way to apply.
What should I do here?
If your question has been marked as a duplicate of this, please find your error message below and apply the fix to your code. The answers usually contain further links to investigate in case it shouldn't be clear from the general answer alone.
If you want to contribute, please add your "favorite" error message, warning or notice, one per answer, a short description what it means (even if it is only highlighting terms to their manual page), a possible solution or debugging approach and a listing of existing Q&A that are of value. Also, feel free to improve any existing answers.
The List
Also see
Source: (StackOverflow)
C# desktop application on express edition. Worked then didn't work 5 seconds later.
I tried the following.
- Ensure debug configuration, debug flag, and full debug info are set on all assemblies.
- Delete all bin and obj folders and all DLLs related to the project from my entire machine.
- Recreate projects causing the problem from scratch.
- Reboot.
I have two WinForms projects in the solution. One of them loads the debug info, one doesn't. They both refer to the assembly I'm trying to get debug info on in exactly the same way in the project file. Any ideas?
I want to add in here, mostly for myself when I come back to review this question, that symbols are not loaded until the assembly is loaded, and the assembly is not loaded until it is needed. If the breakpoint is in a library that is only used in one function in your main assembly, the symbols will not be loaded (and it will show the breakpoint as not being hit) until that function is called.
Source: (StackOverflow)
I am attempting to debug an application on a Motorola Droid, but I am having some difficulty connecting to the device via USB. My development server is a Windows 7 64-bit VM running in Hyper-V, and so I cannot connect directly via USB in the guest or from the host.
I installed a couple of different USB-over-TCP solutions, but the connection appears to have issues since the ADB monitor reports "devicemonitor failed to start monitoring" repeatedly. Is there a way to connect directly from the client on the development machine to the daemon on the device using the network instead of the USB connection or possibly another viable options?
Source: (StackOverflow)
How do I print debug messages in the Google Chrome JavaScript Console?
Please note that the JavaScript Console is not the same as the JavaScript Debugger; they have different syntaxes AFAIK, so the print command in JavaScript Debugger will not work here. In the JavaScript Console, print() will send the parameter to the printer.
Source: (StackOverflow)
How do you debug PHP scripts?
I am aware of basic debugging such as using the Error Reporting. The breakpoint debugging in PHPEclipse is also quite useful.
What is the best (in terms of fast and easy) way to debug in phpStorm or any other IDE?
Source: (StackOverflow)
So what I'm looking for here is something like PHP's print_r function. This is so I can debug my scripts by seeing what's the state of the object in question.
Source: (StackOverflow)
How can I print a message to the error console, preferably including a variable?
For example, something like:
print('x=%d', x);
Source: (StackOverflow)
I want to force the chrome debugger to break on a line via code, or else using some sort of comment tag such as something like console.break().
Is there a way to do this?
Source: (StackOverflow)
I'm developing a C++ command-line application in Visual Studio and need to debug it with command-line arguments. At the moment I just run the generated EXE file with the arguments I need (like this program.exe -file.txt) , but this way I can't debug. Is there somewhere I can specify the arguments for debugging?
Source: (StackOverflow)
So, I started learning to code in Python and later Django. The first times it was hard looking at tracebacks and actually figure out what I did wrong and where the syntax error was. Some time has passed now and some way along the way, I guess I got a routine in debugging my Django code. As this was done early in my coding experience, I sat down and wondered if how I was doing this was ineffective and could be done faster. I usually manage to find and correct the bugs in my code, but I wonder if I should be doing it faster?
I usually just use the debug info Django gives when enabled. When things do end up as I thought it would, I break the code flow a lot with a syntax error, and look at the variables at that point in the flow to figure out, where the code does something other than what I wanted.
But can this be improved? Are there some good tools or better ways to debug your Django code?
Source: (StackOverflow)
I am using the perfmon windows utility to debug memory leaks in a process.
Perfmon explanation:
Working Set- Working Set is the current size, in bytes, of the Working Set of this process. The Working Set is the set of memory pages touched recently by the threads in the process. If free memory in the computer is above a threshold, pages are left in the Working Set of a process even if they are not in use. When free memory falls below a threshold, pages are trimmed from Working Sets. If they are needed they will then be soft-faulted back into the Working Set before leaving main memory.
Virtual Bytes- Virtual Bytes is the current size, in bytes, of the virtual address space the process is using. Use of virtual address space does not necessarily imply corresponding use of either disk or main memory pages. Virtual space is finite, and the process can limit its ability to load libraries.
Private Bytes- Private Bytes is the current size, in bytes, of memory that this process has allocated that cannot be shared with other processes.
Q1. Is it the Private Bytes which I should measure to be sure if the process is having any leaks as it does not involve any shared libraries and any leaks if happening will come from the process itself?
Q2. What is the total memory consumed by the process? Is it the Virtual Bytes or is it the sum of Virtual Bytes and Working Set
Q3. Is there any relation between Private Bytes, Working Set and Virtual Bytes.
Q4. Any tool which gives a better idea memory information?
Source: (StackOverflow)
This question already has an answer here:
When debugging in PHP, I frequently find it useful to simply stick a var_dump() in my code to show me what a variable is, what its value is, and the same for anything that it contains.
What is a good Python equivalent for this?
Source: (StackOverflow)