Re: Optimize causes an error.

[Daniel Lohmann <daniel dot lohmann at informatik dot uni-erlangen dot de>]

LWATCDR schrieb:

> And now for a simple question. How the heck to I find out how much
> free memory I have in c?
> None of the programmers at my office know because we haven't needed to
> check for free memory for many years.

Unfortunately this isn't actually a simple question. On all modern 
operating systems, memory is a highly virtualized resource. From the 
viewpoint of a single process, a concept such as "free memory" just does 
not exist, there is just free address space.

You looking for the available physical RAM?
Well, this should be close to zero on a good OS; such OS tries to use all 
unused physical memory for caching and buffering and frees it on demand, 
that is, if there is a better purpose to use it.

You are looking for the available virtual memory?
Well, this is, in theory, only limited by the size of your address space. 
Thus, you have four GB on a 32bit architecture. The upper one or two GB are 
typically used by the OS itself.

You are looking for the available memory on the C heap?
Well, this is, again, just limited by the available address space. On most 
systems the heap starts with 1 MB of address space, but is expanded by the 
OS/C library on demand.

Moreover, most OS implement working set policies, effectively restricting 
the amount of phyiscal RAM that can be used by a single process. However, 
working sets are highly dynamical, the OS expands and trims them depending 
on load, access characteristics and so on.

As you can see, all this has almost nothing to do with C. It is a highly 
OS-specific thing.

Daniel