This chapter provides reference information for the memory manager. The memory manager API is declared in the header file MemoryMgr.h.
For more information on the memory manager, see the chapter "Memory" in the Palm OS Programmer's Companion, vol. I.
Memory Manager Functions

MemCardInfo

Purpose
Return information about a memory card.
Prototype
Err MemCardInfo (UInt16 cardNo, Char* cardNameP, Char* manufNameP, UInt16* versionP, UInt32* crDateP, UInt32* romSizeP, UInt32* ramSizeP, UInt32* freeBytesP)
Parameters
cardNameP | Pointer to character array (32 bytes), or 0. |
manufNameP | Pointer to character array (32 bytes), or 0. |
versionP | Pointer to version variable, or 0. |
crDateP | Pointer to creation date variable, or 0. |
romSizeP | Pointer to ROM size variable, or 0. |
ramSizeP | Pointer to RAM size variable, or 0. |
freeBytesP | Pointer to free byte-count variable, or 0. |
Result
Returns 0 if no error.
Comments
Pass 0 for those variables that you don't want returned.
MemCmp

Purpose
Compare two blocks of memory.
NOTE: Blocks are compared as unsigned bytes.
Prototype
Int16 MemCmp (const void* s1, const void* s2, Int32 numBytes)
Parameters
s1, s2 | Pointers to block of memory. |
numBytes | Number of bytes to compare. |
Result
Zero if they match, non-zero if not:
+ if s1 > s2
- if s1 < s2
Compatibility
Implemented only if 2.0 New Feature Set is present.
MemCmp can be used to test the equality of blocks in memory on all versions that support MemCmp; however, testing the sort ordering of blocks in memory works reliably only on Palm OS® versions 3.5 and higher. On versions earlier than 3.2, MemCmp always returns a positive value if the blocks are unequal. On versions 3.2 and 3.3, MemCmp reliably returns positive to indicate s1 > s2 and negative to indicate s1 < s2 only if the characters that differ are less than 128 apart. If the difference is greater than that, MemCmp may return positive when it should return negative and vice versa.
MemDebugMode

Purpose
Return the current debugging mode of the memory manager.
Prototype
UInt16 MemDebugMode (void)
Parameters
No parameters.
Result
Returns debug flags as described for MemSetDebugMode.
MemHandleCardNo

Purpose
Return the card number a chunk resides in.
Prototype
UInt16 MemHandleCardNo (MemHandle h)
Parameters
Result
Returns the card number.
Comments
Call this routine to retrieve the card number (0 or 1) a movable chunk resides on.
See Also
MemPtrCardNo
MemHandleDataStorage

Purpose
Return true if the given handle is part of a data storage heap. If not, it's a handle in the dynamic heap.
Prototype
Boolean MemHandleDataStorage (MemHandle h)
Parameters
Result
Returns true if the handle is part of a data storage heap.
Comments
Called by Fields package routines to determine if they need to worry about data storage write-protection when editing a text field.
See Also
MemPtrDataStorage
MemHandleFree

Purpose
Dispose of a movable chunk.
Prototype
Err MemHandleFree (MemHandle h)
Parameters
Result
Returns 0 if no error, or memErrInvalidParam if an error occurs.
Comments
Call this routine to dispose of a movable chunk.
See Also
MemHandleNew
MemHandleHeapID

Purpose
Return the heap ID of a chunk.
Prototype
UInt16 MemHandleHeapID (MemHandle h)
Parameters
Result
Returns the heap ID of a chunk.
Comments
Call this routine to get the heap ID of the heap a chunk resides in.
See Also
MemPtrHeapID
MemHandleLock

Purpose
Lock a chunk and obtain a pointer to the chunk's data.
Prototype
MemPtr MemHandleLock (MemHandle h)
Parameters
Result
Returns a pointer to the chunk.
Comments
Call this routine to lock a chunk and obtain a pointer to the chunk.
MemHandleLock and MemHandleUnlock should be used in pairs.
See Also
MemHandleNew, MemHandleUnlock
MemHandleNew

Purpose
Allocate a new movable chunk in the dynamic heap and returns a handle to it.
Prototype
MemHandle MemHandleNew (UInt32 size)
Parameters
-> size | The desired size of the chunk. |
Result
Returns a handle to the new chunk, or 0 if unsuccessful.
Comments
Use this call to allocate dynamic memory. Before you can write data to the memory chunk that MemHandleNew allocates, you must call MemHandleLock to lock the chunk and get a pointer to it.
See Also
MemPtrFree, MemPtrNew, MemHandleFree, MemHandleLock
MemHandleResize

Purpose
Resize a chunk.
Prototype
Err MemHandleResize (MemHandle h, UInt32 newSize)
Parameters
-> newSize | The new desired size. |
Result
memErrInvalidParam | Invalid parameter passed. |
memErrNotEnoughSpace | Not enough free space in heap to grow chunk. |
memErrChunkLocked | Can't grow chunk because it's locked. |
Comments
Call this routine to resize a chunk. This routine is always successful when shrinking the size of a chunk, even if the chunk is locked. When growing a chunk, it first attempts to grab free space immediately following the chunk so that the chunk does not have to move. If the chunk has to move to another free area of the heap to grow, it must be movable and have a lock count of 0.
On devices running version 2.0 or earlier of Palm OS, the MemHandleResize function tries to resize the chunk only within the same heap, whereas DmResizeRecord will look for space in other data heaps if it can't find enough space in the original heap.
See Also
MemHandleNew, MemHandleSize
MemHandleSetOwner

Purpose
Set the owner ID of a chunk.
Prototype
Err MemHandleSetOwner (MemHandle h, UInt16 owner)
Parameters
-> owner | New owner ID of the chunk. Specify 0 to set the owner to the operating system. |
Result
Returns 0 if no error, or memErrInvalidParam if an error occurs.
Comments
When you allocate a parameter block to pass to SysUIAppSwitch or SysAppLaunch, you must call MemPtrSetOwner to grant ownership of the parameter block chunk to the OS (your application is originally set as the owner). If the parameter block structure references any chunks by handle, you also must call MemHandleSetOwner to grant ownership of those blocks to the OS. If you don't change the ownership of these chunks, they will get freed before the application you're launching has a chance to use them.
MemHandleSize

Purpose
Return the requested size of a chunk.
Prototype
UInt32 MemHandleSize (MemHandle h)
Parameters
Result
Returns the requested size of the chunk.
Comments
Call this routine to get the size originally requested for a chunk.
See Also
MemHandleResize
MemHandleToLocalID

Purpose
Convert a handle into a local chunk ID which is card relative.
Prototype
LocalID MemHandleToLocalID (MemHandle h)
Parameters
Result
Returns local ID, or NULL (0) if unsuccessful.
Comments
Call this routine to convert a chunk handle to a local ID.
See Also
MemLocalIDToGlobal, MemLocalIDToLockedPtr
MemHandleUnlock

Purpose
Unlock a chunk given a chunk handle.
Prototype
Err MemHandleUnlock (MemHandle h)
Parameters
Result
memErrInvalidParam | Invalid parameter passed. |
Comments
Call this routine to decrement the lock count for a chunk.
MemHandleLock and MemHandleUnlock should be used in pairs.
See Also
MemHandleLock
MemHeapCheck

Purpose
Check validity of a given heap.
Prototype
Err MemHeapCheck (UInt16 heapID)
Parameters
heapID | ID of heap to check. |
Result
Returns 0 if no error.
See Also
MemDebugMode, MemSetDebugMode
MemHeapCompact

Purpose
Compact a heap.
Prototype
Err MemHeapCompact (UInt16 heapID)
Parameters
-> heapID | ID of the heap to compact. |
Result
Always returns 0.
Comments
Most applications never need to call this function explicitly. The system software calls this function at various times; for example, during memory allocation (if sufficient free space is not available) and during system reboot.
Call this routine to compact a heap and merge all free space. This routine attempts to move all movable chunks to the start of the heap and merge all free space in the center of the heap.
MemHeapDynamic

Purpose
Return true if the given heap is a dynamic heap.
Prototype
Boolean MemHeapDynamic (UInt16 heapID)
Parameters
heapID | ID of the heap to be tested. |
Result
Returns true if dynamic, false if not.
Comments
Dynamic heaps are used for volatile storage, application stacks, globals, and dynamically allocated memory.
NOTE: In Palm OS 3.5, the dynamic heap is sized based on the amount of memory available, and is generally larger than before.
See Also
MemNumHeaps, MemHeapID
MemHeapFlags

Purpose
Return the heap flags for a heap.
Prototype
UInt16 MemHeapFlags (UInt16 heapID)
Parameters
Result
Returns the heap flags.
Comments
Call this routine to retrieve the heap flags for a heap. The flags can be examined to determine if the heap is ROM based or not. ROM-based heaps have the memHeapFlagReadOnly bit set (the memHeapFlagReadOnly mask has a value of 0x0001).
See Also
MemNumHeaps, MemHeapID
MemHeapFreeBytes

Purpose
Return the total number of free bytes in a heap and the size of the largest free chunk in the heap.
Prototype
Err MemHeapFreeBytes (UInt16 heapID, UInt32* freeP, UInt32* maxP)
Parameters
<-> freeP | Pointer to a variable of type UInt32 for free bytes. |
<-> maxP | Pointer to a variable of type UInt32 for max free chunk size. Do not pass NULL for this argument. |
Result
Always returns 0.
Comments
This routine doesn't compact the heap but may be used to determine in advance whether an allocation request will succeed. Before allocating memory, call this function and test the value returned in maxP to determine whether enough free space to fulfill your allocation request exists. If not, you may make more space available by calling the MemHeapCompact function. Note that both MemPtrNew and MemHandleNew automatically compact the heap if necessary.
See Also
MemHeapSize, MemHeapID, MemHeapCompact
MemHeapID

Purpose
Return the heap ID for a heap, given its index and the card number.
Prototype
UInt16 MemHeapID (UInt16 cardNo, UInt16 heapIndex)
Parameters
-> cardNo | The card number, either 0 or 1. |
-> heapIndex | The heap index, anywhere from 0 to MemNumHeaps - 1. |
Result
Returns the heap ID.
Comments
Call this routine to retrieve the heap ID of a heap, given the heap index and the card number. A heap ID must be used to obtain information on a heap such as its size, free bytes, etc., and is also passed to any routines which manipulate heaps.
See Also
MemNumHeaps
MemHeapScramble

Purpose
Scramble the specified heap.
Prototype
Err MemHeapScramble (UInt16 heapID)
Parameters
heapID | ID of heap to scramble. |
Comments
The system attempts to move each movable chunk.
Useful for debugging.
Result
Always returns 0.
See Also
MemDebugMode, MemSetDebugMode
MemHeapSize

Purpose
Return the total size of a heap including the heap header.
Prototype
UInt32 MemHeapSize (UInt16 heapID)
Parameters
Result
Returns the total size of the heap.
See Also
MemHeapFreeBytes, MemHeapID
MemLocalIDKind

Purpose
Return whether or not a local ID references a handle or a pointer.
Prototype
LocalIDKind MemLocalIDKind (LocalID local)
Parameters
-> local | Local ID to query |
Result
Returns LocalIDKind, or a memIDHandle or memIDPtr (see MemoryMgr.h).
Comments
This routine determines if the given local ID is to a nonmovable (memIDPtr) or movable (memIDHandle) chunk.
MemLocalIDToGlobal

Purpose
Convert a local ID, which is card relative, into a global pointer in the designated card.
Prototype
MemPtr MemLocalIDToGlobal (LocalID local, UInt16 cardNo)
Parameters
-> local | The local ID to convert. |
-> cardNo | Memory card the chunk resides in. |
Result
Returns pointer or handle to chunk.
See Also
MemLocalIDKind, MemLocalIDToLockedPtr
MemLocalIDToLockedPtr

Purpose
Return a pointer to a chunk given its local ID and card number.
If the local ID references a movable chunk handle, this routine automatically locks the chunk before returning.
Prototype
MemPtr MemLocalIDToLockedPtr (LocalID local, UInt16 cardNo)
Parameters
Result
Returns pointer to chunk, or 0 if an error occurs.
See Also
MemLocalIDToGlobal, MemLocalIDToPtr, MemLocalIDKind, MemPtrToLocalID, MemHandleToLocalID
MemLocalIDToPtr

Purpose
Return pointer to chunk, given the local ID and card number.
Prototype
MemPtr MemLocalIDToPtr (LocalID local, UInt16 cardNo)
Parameters
-> local | Local ID to query. |
-> cardNo | Card number the chunk resides in. |
Result
Returns a pointer to the chunk, or 0 if error.
Comments
If the local ID references a movable chunk and that chunk is not locked, this function returns 0 to indicate an error.
See Also
MemLocalIDToGlobal, MemLocalIDToLockedPtr
MemMove

Purpose
Move a range of memory to another range in the dynamic heap.
Prototype
Err MemMove (void* dstP, const void* sP, Int32 numBytes)
Parameters
dstP | Pointer to destination. |
numBytes | Number of bytes to move. |
Result
Always returns 0.
Comments
Handles overlapping ranges.
For operations where the destination is in a data heap, see DmSet, DmWrite, and related functions.
MemNumCards

Purpose
Return the number of memory card slots in the system. Not all slots need to be populated.
Prototype
UInt16 MemNumCards (void)
Parameters
None.
Result
Returns number of slots in the system.
MemNumHeaps

Purpose
Return the number of heaps available on a particular card.
Prototype
UInt16 MemNumHeaps (UInt16 cardNo)
Parameters
-> cardNo | The card number; either 0 or 1. |
Result
Number of heaps available, including ROM- and RAM-based heaps.
Comments
Call this routine to retrieve the total number of heaps on a memory card. The information can be obtained by calling MemHeapSize, MemHeapFreeBytes, and MemHeapFlags on each heap using its heap ID. The heap ID is obtained by calling MemHeapID with the card number and the heap index, which can be any value from 0 to MemNumHeaps.
MemNumRAMHeaps

Purpose
Return the number of RAM heaps in the given card.
Prototype
UInt16 MemNumRAMHeaps (UInt16 cardNo)
Parameters
Result
Returns the number of RAM heaps.
See Also
MemNumCards
MemPtrCardNo

Purpose
Return the card number (0 or 1) a nonmovable chunk resides on.
Prototype
UInt16 MemPtrCardNo (MemPtr p)
Parameters
-> p | Pointer to the chunk. |
Result
Returns the card number.
See Also
MemHandleCardNo
MemPtrDataStorage

Purpose
Return true if the given pointer is part of a data storage heap; if not, it is a pointer in the dynamic heap.
Prototype
Boolean MemPtrDataStorage (MemPtr p)
Parameters
Result
Returns true if the chunk is part of a data storage heap.
Comments
Called by Fields package to determine if it needs to worry about data storage write-protection when editing a text field.
See Also
MemHeapDynamic
MemPtrFree

Purpose
Macro to dispose of a chunk.
Prototype
Err MemPtrFree (MemPtr p)
Parameters
Result
0 | If no error or memErrInvalidParam (invalid parameter). |
Comments
Call this routine to dispose of a nonmovable chunk.
MemPtrHeapID

Purpose
Return the heap ID of a chunk.
Prototype
UInt16 MemPtrHeapID (MemPtr p)
Parameters
-> p | Pointer to the chunk. |
Result
Returns the heap ID of a chunk.
Comments
Call this routine to get the heap ID of the heap a chunk resides in.
MemPtrNew

Purpose
Allocate a new nonmovable chunk in the dynamic heap.
Prototype
MemPtr MemPtrNew (UInt32 size)
Parameters
-> size | The desired size of the chunk. |
Result
Returns pointer to the new chunk, or 0 if unsuccessful.
Comments
This routine allocates a nonmovable chunk in the dynamic heap and returns a pointer to the chunk. Applications can use it when allocating dynamic memory.
In Palm OS 3.5, the dynamic heap is sized based on the amount of memory available, and is generally larger than before.
NOTE: You cannot allocate a zero-size reference block.
MemPtrRecoverHandle

Purpose
Recover the handle of a movable chunk, given a pointer to its data.
Prototype
MemHandle MemPtrRecoverHandle (MemPtr p)
Parameters
-> p | Pointer to the chunk. |
Result
Returns the handle of the chunk, or 0 if unsuccessful.
Comments
Don't call this function for pointers in ROM or nonmovable data chunks.
MemPtrResize

Purpose
Resize a chunk.
Prototype
Err MemPtrResize (MemPtr p, UInt32 newSize)
Parameters
-> p | Pointer to the chunk. |
-> newSize | The new desired size. |
Result
Returns 0 if no error, or memErrNotEnoughSpace memErrInvalidParam, or memErrChunkLocked if an error occurs.
Comments
Call this routine to resize a locked chunk. This routine is always successful when shrinking the size of a chunk. When growing a chunk, it attempts to use free space immediately following the chunk.
See Also
MemPtrSize, MemHandleResize
MemPtrSetOwner

Purpose
Set the owner ID of a chunk.
Prototype
Err MemPtrSetOwner (MemPtr p, UInt16 owner)
Parameters
-> p | Pointer to the chunk. |
-> owner | New owner ID of the chunk. Specify 0 to set the owner to the operating system. |
Result
Returns 0 if no error, or memErrInvalidParam if an error occurs.
Comments
When you allocate a parameter block to pass to SysUIAppSwitch or SysAppLaunch, you must call MemPtrSetOwner or MemHandleSetOwner to grant ownership of the parameter block chunk, and any other chunks referenced in it, to the OS (your application is originally set as the owner). If you don't change the ownership of the parameter block, it will get freed before the application you're launching has a chance to use it.
MemPtrSize

Purpose
Return the size of a chunk.
Prototype
UInt32 MemPtrSize (MemPtr p)
Parameters
-> p | Pointer to the chunk. |
Result
The requested size of the chunk.
Comments
Call this routine to get the original requested size of a chunk.
MemPtrToLocalID

Purpose
Convert a pointer into a card-relative local chunk ID.
Prototype
LocalID MemPtrToLocalID (MemPtr p)
Parameters
Result
Returns the local ID of the chunk.
Comments
Call this routine to convert a chunk pointer to a local ID.
See Also
MemLocalIDToPtr
MemPtrUnlock

Purpose
Unlock a chunk, given a pointer to the chunk.
Prototype
Err MemPtrUnlock (MemPtr p)
Parameters
Result
0 if no error, or memErrInvalidParam if an error occurs.
Comments
A chunk must not be unlocked more times than it was locked.
See Also
MemHandleLock
MemSet

Purpose
Set a memory range in a dynamic heap to a specific value.
Prototype
Err MemSet (void* dstP, Int32 numBytes, UInt8 value)
Parameters
dstP | Pointer to the destination. |
numBytes | Number of bytes to set. |
Result
Always returns 0.
Comments
For operations where the destination is in a data heap, see DmSet, DmWrite, and related functions.
MemSetDebugMode

Purpose
Set the debugging mode of the memory manager.
Prototype
Err MemSetDebugMode (UInt16 flags)
Parameters
Comments
Use the logical OR operator (|) to provide any combination of one, more, or none of the following flags:
memDebugModeCheckOnChange memDebugModeCheckOnAll memDebugModeScrambleOnChange memDebugModeScrambleOnAll memDebugModeFillFree memDebugModeAllHeaps memDebugModeRecordMinDynHeapFree
Result
Returns 0 if no error, or -1 if an error occurs.
MemStoreInfo

Purpose
Return information on either the RAM store or the ROM store for a memory card.
Prototype
Err MemStoreInfo (UInt16 cardNo, UInt16 storeNumber, UInt16* versionP, UInt16* flagsP, Char* nameP, UInt32* crDateP, UInt32* bckUpDateP, UInt32* heapListOffsetP, UInt32* initCodeOffset1P, UInt32* initCodeOffset2P, LocalID* databaseDirIDP)
Parameters
-> cardNo | Card number, either 0 or 1. |
-> storeNumber | Store number; 0 for ROM, 1 for RAM. |
<-> versionP | Pointer to version variable, or 0. |
<-> flagsP | Pointer to flags variable, or 0. |
<-> nameP | Pointer to character array (32 bytes), or 0. |
<-> crDateP | Pointer to creation date variable, or 0. |
<-> bckUpDateP | Pointer to backup date variable, or 0. |
<-> heapListOffsetP | Pointer to heapListOffset variable, or 0. |
<-> initCodeOffset1P | Pointer to initCodeOffset1 variable, or 0. |
<-> initCodeOffset2P | Pointer to initCodeOffset2 variable, or 0. |
<-> databaseDirIDP | Pointer to database directory chunk ID variable, or 0. |
Result
Returns 0 if no error, or memErrCardNotPresent, memErrRAMOnlyCard, or memErrInvalidStoreHeader if an error occurs.
Comments
Call this routine to retrieve any or all information on either the RAM store or the ROM store for a card. Pass 0 for variables that you don't wish returned.
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