6600putz%ucsbuxa@hub.ucsb.edu (11/22/89)
Does Turbo Pascal (TP compiled programs) automatically dispose of all dynamically allocated memory created during execution of the program, or do I, the programmer, have to manually dispose of this memory, at the end of the program? I have a linked-list set up and of course wish to dispose of all the memory allocated to its use at the close of my program after saving the data file. If this is in the manual, I missed it... Scott Kral UCSB
unkydave@shumv1.uucp (David Bank) (11/22/89)
In article <21510@adm.BRL.MIL> 6600putz%ucsbuxa@hub.ucsb.edu writes: > > Does Turbo Pascal (TP compiled programs) automatically dispose of all >dynamically allocated memory created during execution of the program, or >do I, the programmer, have to manually dispose of this memory, at the >end of the program? I have a linked-list set up and of course wish to >dispose of all the memory allocated to its use at the close of my program >after saving the data file. If this is in the manual, I missed it... > > Scott Kral > UCSB My response is based on TP 3.0, as I do not (yet) have extensive experience with TP 4.0 or 5.0 (one of these days I'll break the shrinkwrap on the latter). Anyway, as I understand dynamic memory allocation on the PC, requests for memory are made to DOS. DOS returns a pointer to the allocated memory or nothing if there was a problem (like no more available memory) Inside your TP program, you can return allocated memory to the heap using the Dispose() standard function. This frees memory as far as both the program and DOS are concerned. If you program terminates and does not stay resident, all memory allocated to that process (program) is immediately returned by DOS to the free heap. Again, the program musn't stay resident. The memory is returned to the heap regardless of whether it was dynamically allocated or not. DOS doesn't care - it belonged to the terminated program, now it is free memory. Hope this helps. Unky Dave unkydave@shumv1.ncsu.edu
dhinds@portia.Stanford.EDU (David Hinds) (11/23/89)
In article <4620@ncsuvx.ncsu.edu>, unkydave@shumv1.uucp (David Bank) writes: > Anyway, as I understand dynamic memory allocation on the PC, > requests for memory are made to DOS. DOS returns a pointer to the > allocated memory or nothing if there was a problem (like no more > available memory) > > Inside your TP program, you can return allocated memory to the > heap using the Dispose() standard function. This frees memory as far > as both the program and DOS are concerned. > Actually, allocating and disposing of memory within a pascal program doesn't go through the DOS memory manager. When your program is loaded by DOS, it is typically given control of all available memory unless you specify otherwise (by compiling with switches to limit memory consumption). After allowing for the space occupied by the program, static variables, and the stack, the rest of the memory DOS has allocated goes for TP's heap. Allocating and disposing dynamic variables is managed by TP's runtime library. When a program terminates, the memory allocated when it was initiated is automatically freed by DOS, so yes, it doesn't matter if you forget to dispose of some variables. As far as entering and exiting a program are concerned, then, it doesn't matter how the allocation is handled. However, it is important that while a program is running, Dispose() doesn't actually return anything to DOS's heap. There won't be any memory available for running another program from within a TP program, regardless of how empty TP's heap may be. Memory has to be explicitly freed for this purpose, either at compile time, or by shrinking a program's DOS memory allocation as soon as it starts to execute. I think there is a TP procedure to do this, but I don't remember the name. The information isn't obvious in the manuals; I think there is an index entry for "memory map" somewhere. - David Hinds dhinds@portia.stanford.edu
unkydave@shumv1.uucp (David Bank) (11/24/89)
To Mr. David Hinds:
In reference to your response about Turbo Pascal dynamic memory
allocation, please specify which version(s) you comments applied to.
It was my understanding, and it may be in error, that dynamic memory
allocation handling underwent significant alteration between versions
3.0 and 4.0 (along with just about everything else).
Thank you.
Unky Dave
unkydave@shumv1.ncsu.edudhinds@portia.Stanford.EDU (David Hinds) (11/25/89)
In article <4645@ncsuvx.ncsu.edu>, unkydave@shumv1.uucp (David Bank) writes: > > It was my understanding, and it may be in error, that dynamic memory > allocation handling underwent significant alteration between versions > 3.0 and 4.0 (along with just about everything else). > My description applies to all versions of TP, as far as I know. I don't remember for sure, but I think the early TP dispose() routine wasn't capable of reclaiming the disposed space for later calls to new(). The newer versions maintain a list of free blocks of memory within the heap. Heap variables are created starting at the base of the heap, and the free list grows downward from the top. The early versions (3.0 or earlier?) didn't maintain a free list. The DOS-level memory allocation is basically the same in all versions. In fact, for early versions of DOS, the "dispose block" routine never worked right, and it would have been disasterous for TP to use it for heap memory management. David Hinds dhinds@portia.stanford.edu
unkydave@shumv1.uucp (David Bank) (11/27/89)
OK, thanks. I wasn't too clear on that. I started programming in Pascal when TP 2.0 came out, but had never investigated that end of it too closely (mainly because I have had little call, thus far, for dynamic memory allocation in Pascal). Unky Dave unkydave@shumv1.ncsu.edu