Memory problems (possibly very easy question)

[hamishd]

Hello,

In my application I create some large vectors to hold data. For
example:

std::vector<DataItemClass*> MyData;
DataItemClass * DataItem;

for(i=0;i<SomeLargeLimit;i++){
DataItem = new DataltemClass;
MyData.push_back(DataItem);
}


So while my application is running, I can watch in the "Windows Task
Manager" under "Processes" my application's mem usage increase as I
allocate more memory. Eg, say to 150,000KB.

How do I release this memory?

I go:
for(i=0;i<MyData.size();i++)
delete(MyData);
MyData.clear();

But my mem usage does not reduce... so when i run the process a few
times the usage gets really really large, and windows gives me virtual
memory usage warnings (or similar).

When I run the application in debug mode, the same thing occurs, and i
can confirm the "delete" operations are being executed. MSVC++ 6.0 does
not show any memory leaks, so why is my memory usage not clearing?

 

[Gavin Deane]

Hello,

In my application I create some large vectors to hold data. For
example:

std::vector<DataItemClass*> MyData;
DataItemClass * DataItem;

for(i=0;i<SomeLargeLimit;i++){
DataItem = new DataltemClass;
MyData.push_back(DataItem);
}


So while my application is running, I can watch in the "Windows Task
Manager" under "Processes" my application's mem usage increase as I
allocate more memory. Eg, say to 150,000KB.

How do I release this memory?

I go:
for(i=0;i<MyData.size();i++)
delete(MyData);
MyData.clear();

What does MyData.capacity() return here. clear erases the elements from
the vector, so after this code MyData.size() will return zero. However,
the memory held by the vector is not necessarily released.

If capacity does not return zero, the vector is keeping hold of its
storage space for future use, as it is allowed to do. The following
trick may help instead of calling clear (but make sure you keep your
loop that deletes all your DataItemClass objects).

std::vector<DataItemClass*>().swap(MyData);

See http://www.gotw.ca/gotw/054.htm

Gavin Deane

 

[Gernot Frisch]

std::vector<DataItemClass*> MyData;
DataItemClass * DataItem;

for(i=0;i<SomeLargeLimit;i++){
DataItem = new DataltemClass;
MyData.push_back(DataItem);
}
for(i=0;i<MyData.size();i++)
delete(MyData);
MyData.clear();

delete without () is enough.
It might be that your OS is not requiring the memory, so it's not
freeing it. this might speed up re-allocations later. Try to open some
other app that really uses a lot of ram and see if it gets freed then.

 

[peter koch]

hamishd skrev:

Hello,

In my application I create some large vectors to hold data. For
example:

std::vector<DataItemClass*> MyData;
DataItemClass * DataItem;

for(i=0;i<SomeLargeLimit;i++){
DataItem = new DataltemClass;
MyData.push_back(DataItem);
}


So while my application is running, I can watch in the "Windows Task
Manager" under "Processes" my application's mem usage increase as I
allocate more memory. Eg, say to 150,000KB.

How do I release this memory?

I go:
for(i=0;i<MyData.size();i++)
delete(MyData);
MyData.clear();

But my mem usage does not reduce... so when i run the process a few
times the usage gets really really large, and windows gives me virtual
memory usage warnings (or similar).

This means there is a problem somewhere.

When I run the application in debug mode, the same thing occurs, and i
can confirm the "delete" operations are being executed. MSVC++ 6.0 does
not show any memory leaks, so why is my memory usage not clearing?

Because you made a fault elsewhere. Can you provide a complete program
to demonstrate your fault? Do that - e.g. providing a dummy
DataItemClass and see if the problem reproduces. If it does, post
again. My suspicion is that the culprit is the DataItemClass
destructor.
By the way: VC++ 6.0 is REALLY old. You ought to replace it with
something more modern and more C++.

/Peter

 

[Eric Hill]

But my mem usage does not reduce... so when i run the process a few

times the usage gets really really large, and windows gives me virtual
memory usage warnings (or similar).

If you minimize the application, does the memory usage drop? If so, have
a look at this article:

http://support.microsoft.com/kb/293215

Eric

 

[Dan Bloomquist]

Interesting. On my machine:

404MB
TC tc;
for( long i= 0; i < 2000000; ++i )
tc.push_back( new CTest );
540MB
for( ITC it= tc.begin( ); it != tc.end( ); ++it )
delete *it;
413MB
{
TC temp;
temp.swap( tc );
}
404MB

Best, Dan.