Thread: free memory in structure

I have a structure which contains multiple dynamic allocated memory.

If I free one of its dynamic allocated memory, can the freed memory be used? Or only when I free the whole structure then the freed memory can be used?

used by the memory manager. an example

Code:

struct opStructure {

int **array1;
int **array2;
}

when I do this "delete [] array1[i][j]" or "delete [] array1[i]", the memory used by the application doesn't drop.

malloc(), calloc(), realloc(), and free() manage raw dynamic memory in C. operators new and delete, among other things, manage raw dynamic memory in C++.

Assuming the application is running on an operating system, dynamic memory (in fact, all memory resources) will ultimately be obtained from the operating system. However, this is no guarantee that free() or operator delete will actually return memory to the operating system. Instead, as vart said, it may simply mark the memory so it can be used again by the operating system --- so the next call to malloc() [in C] or operator new (in C++) may simply reuse memory rather than having to ask the operating system for it. The reason for this is that the act of obtaining memory from the operating system is relatively expensive, so these sorts of tricks are a performance optimisation. The actual techniques used depend on the compiler, the implementation of its library, and the operating system.

But the net effect is that, if you are monitoring memory usage by your program, neither calling free() or invoking operator delete are guaranteed to immediately result in the application using less memory. However, if you watch, you will often find that subsequent usage of malloc() or operator new() will not necessarily result in the application using more memory.

thanks for the advises guys!

I suspect my application sometimes run out of address space and I will have error when using using new []. Any suggestions or advice how to detect the address space is running out?

You should catch the exception, free some memory, and try again.

ok, so i should write the exception for the new[] on my own source code?

>> i should write the exception for the new[] on my own source code?
Do you mean throw or catch the exception? Are you familiar with exceptions?

Handling memory errors is tricky. If you have a certain part of the code where you think you will run out of memory and you can free memory if you need to, then simply create a loop or a couple of if blocks that try a couple times to get memory. The first attempt should be in a try/catch block. If it fails, then free some memory and try again. The second attempt should also probably be in a try/catch block so you can exit the program gracefully.

nope, i'm not familiar with exceptions, I thought it is more common in Java, but i roughly get what you mean =)