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Closed 11 years ago.
It seems like the bugs in my project are evolving. While in the beginning time, causers of program crashes were easily to spot using the debugger (the line it points to after the program crashes), it's different now.
Many bugs cause the program to crash in completely arbitary places not even closely related to them.
How can I spot bugs "hiding" from the debugger in a better way?
(I use Visual Studio 2010)
Profile your code for memory corruption, memory overwrites and memory leaks.
Root cause analysis.
When you find an obvious bug, don't just fix the bug, fix the coding style that allowed it.
If you have any code using raw memory and pointers, replace it by memory allocated using std::vector and its iterators. It will compile to exactly the same speedy code in Release mode, but in Debug mode it will used checked iterators, which will catch some bugs as early as possible.
Use memory corruption checking utilities, like gflags or debug heap. "Floating" crushes almost always come from corrupted memory in C++ programs
Related
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Closed 9 years ago.
I am aware about the risks on race conditions and that values written or read might be corrupted. I am in a situation where I have races on boolean and integers and a couple of classes instance.
Could this lead to a program crash, or any other nasty effect on my program aside from the data not being valid? Do I have worry for the worst?
I have 2 versions of my program a debug and another with a lot of options for optimization. I am worried about this last one as it goes to production.
data not being valid may result in anything (i.e. you invoke undefined behavior). So having that in mind your application may crash, leak memory, format you hard drive and almost anything else.
Could this lead to a program crash
Depends on the resource being raced for, but yes. If one thread grabs the resource and another thread needs it to progress, you can get undefined behavior and even program crashes.
any other nasty effect on my program aside from the data not being valid?
Aside from invalid data (thus a practically useless program), you could also be prone to deadlocks.
The wikipedia article on race condition is a good place to find answers to questions such as these.
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Closed 10 years ago.
I went through so many topics asking about "Why does release build fail and not debug?", but I'm across a situation where it's reverse.
Here release build works fine but Debug mode build breaks.
What are possible reasons or situations where this can happen?
Any reply is appreciated.
Thanks in advance.
One of our friend gave some direction towards memory freeing issue..
This is the same thing i'm facing...
When I build in release mode it build successfully, but when I try to build in debug mode it fails/breaks at a point where there is statement for freeing up the allocated memory..
code is like: check if buffer is null, and free it if it's not null...
if(buffer){
free(buffer)
}
When I keep breakpoint on that line (inside if loop) and check value in debug mode, it appears as "bad pointer".(0x000000)
but then question remains like why it went inside of if-loop even though buffer has value 0x000000 ?
I don't know the details about your environment, but some debug environments take extra steps to trigger bugs (e.g. filling freed memory with invalid data), whereas the release build does not, giving you more chances to get lucky.
The problem is that your luck tends to run out when you move up from test data into a real environment....
I would suggest that if you are using visual studio, probably you have different configurations (linker, libraries, paths, etc.) for different profiles: Debug, Release. In general this IDE, like Visual Studio, come with this type of GUI configuration for those modes.
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Closed 11 years ago.
I have a really nasty bug in my program, which grew quite complex over time. It's probably the worst bug I've ever had.
I think that it might be related to a static variable initialization fiasco, but how can I ensure myself of that?
When the bug strikes, the program crashes due to heap corruption at a random point after startup, but far inside the main() function.
To be honest, I don't know what to do.
I'm on Windows 7 using Microsoft Visual Studio 2010
my program, which grew quite complex
over time
Do you keep backups of previous versions?
Find an older version that worked and continue working based on that version...
There is a famous quote out there:
"Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." --Brian Kernighan
If this program has become more complicated than you can handle then it may be time to think about refactoring.
(This is in no way intended to be demeaning or to be taken as a personal attack...)
Run your program in the debugger, and step through the code until you see what's wrong. Place breakpoints liberally anywhere you think the bug might be caused.
Try debugging your program with gdb.
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Closed 12 years ago.
So I mean like it tries to educate it self and collects some data... Are there any such points/feilds in encoding part of ffmpeg (that I hope can be disabeld)?
BTW: My problem is simple: I looked thrue out all my code. It seriosly looks like it is some part of my ffmpeg windows build leaks memory a littel... all the time while I am encoding... So I hope ffmpeg is just triing to learn so that I would be able to tell ti not to learn!)
FFmpeg libraries use a very object-oriented design. All memory allocated should be kept track of in the context structures and freed when the relevant context is destroyed. There may be some one-time allocation and initialization of constant global data which one could call a "leak", but I believe that was all replaced with static const tables to facilitate better use of shared memory and eliminate memory leaks associated with dynamic loading. If you really think it's leaking (and if you care), you need to use some memory debugging tools to identify where the leaks might be and coordinate finding/fixing them with the developers.
If what you mean is that during a single encode, memory usage grows slightly, this is probably normal and to be expected. It shouldn't be much, and the memory should all be released when the encoding context is freed.
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Closed 12 years ago.
This is a further question for my previous one here.
Is there a general solution for this?
Fix all dangling pointers
Fix all buffer overflows
Use pointers only where they are really needed
Reading your original post I'm not 100% you are facing a heap-corruption and you really hope you don't because if you would this is one of the most tricky errors to track down and AFAIK there are no solutions that always work.
However, if you are positive its a heap-corruption and you are on the windows platform you could try out the tool gflags. This advanced debugging tools allow you to install a debug heap manager in order to make it possible to find certain kinds of heap corruptions. One of the neat options it has is to make each allocation in it's own page or to write protect the heap datastructures. This makes it easier to pinpoint the exact location of the heap-corruption. It sucks lots of memory and CPU though.
Another tip if you are using Visual Studio is that if you manage to find that something is corrupting the data after a certain point of time and you wish to find the code that corrupts the data you can use Data Breakpoint to break whenever someone changes the data in question.
I wish you good luck.
Adding to swegi's answer I would check all your C++ constructors and all C initializations. Transform all dynamic C++ constructors (those where you put the init code in the function body) into static ones (where you initialize with the special constructor syntax). And be sure that you init all pointers and pointer members to 0. For C, I would initialize all variables.
Then, on unix I would use valgrind, usually this is quite good in finding all access violations and if you compile with all debugging options on it is able to trace it to the source line. There should be something similar on windows, too.