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memory leak
Jan 17, 2011 at 7:58pm
Hey guys,
I'm trying to understand memory leaks better. Specifically, a program (numerical simulation) seems to have a small memory leak despite me avoiding raw pointers as much as possible. The thing I'm confused about is the free system memory decreases as the program runs (the leak), but doesn't bounce back up after the program terminates. I thought that even if there was a leak the program termination would release the memory back to the operating system. What am I missing here?
I'm trying to understand memory leaks better. Specifically, a program (numerical simulation) seems to have a small memory leak despite me avoiding raw pointers as much as possible. The thing I'm confused about is the free system memory decreases as the program runs (the leak), but doesn't bounce back up after the program terminates. I thought that even if there was a leak the program termination would release the memory back to the operating system. What am I missing here?
Jan 17, 2011 at 8:09pm
No, if you allocate memory yourself with new, it is not available to the operating system until delete has been called on the pointer. So if you ran your program enough times (although it would probably be lots and lots) then your computer would run out of available memory and crash.
Jan 17, 2011 at 8:22pm| No, if you allocate memory yourself with new, it is not available to the operating system until delete has been called on the pointer. |
Why not? AFAIK, modern operating systems would clean it up.
Jan 17, 2011 at 8:32pm
It is available after the program terminates on every operating system I have ever used. This is usually a case of misreading or misinterpreting what the OS is telling you about free memory.
Jan 17, 2011 at 8:37pm
Oh really? Damn it I'm telling people a lot of wrong information in the last few days =S I'm learning things I suppose
Jan 17, 2011 at 10:14pm
Hmm, I must be doing something really evil then, since it definitely is not freeing the memory. The big leak that (I think) I fixed was pretty nasty. In the simulation I dump the current system state to file often, via a statement like
fprintf(f, "%Lf, %Lf", a, b)
Now if somehow a and b are not actually longs e.g. regular doubles instead of long doubles, it memory leaks! Most evil problem ever. Who heard of a memory leak in a print statement.
fprintf(f, "%Lf, %Lf", a, b)
Now if somehow a and b are not actually longs e.g. regular doubles instead of long doubles, it memory leaks! Most evil problem ever. Who heard of a memory leak in a print statement.
Jan 17, 2011 at 10:53pm
if they are not longs, the function can't tell and might be accessing memory that it shouldn't. that's why the '...' are evil...
Jan 17, 2011 at 10:56pm
Look up varargs (ellipsis) and all the problems associated with them. Learn them, the avoid them whenever you can.. well, unless you need them (you are on a project that uses functions with them or something), but then you'll know the problems associated with them.
Jan 17, 2011 at 10:57pm
they say there is over 1000 ways you can shoot yourself in the foot with c++. looks like you just found way 423
Jan 17, 2011 at 11:03pm
they are actually handy when you have no other choice, but there is no checking... you have to trust the programmer using your code not to mess it up.
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