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IDL

Freeing Pointers

Freeing Pointers

The PTR_FREE procedure destroys the heap variables pointed at by pointers supplied as its arguments. Any memory used by the heap variable is released, and the heap variable ceases to exist. PTR_FREE is the only way to destroy a pointer heap variable; if PTR_FREE is not called on a heap variable, it continues to exist until the IDL session ends, even if no pointers remain to reference it.

Note that the pointers themselves are not destroyed. Pointers that point to nonexistent heap variables are known as dangling references, and are discussed in more detail in Dangling References.

See PTR_FREEfor further details.

The HEAP_FREE procedure recursively frees all heap variables (pointers or objects) referenced by its input argument. This routine examines the input variable, including all array elements and structure fields. When a valid pointer or object reference is encountered, that heap variable is marked for removal, and then is recursively examined for additional heap variables to be freed. In this way, all heap variables that are referenced directly or indirectly by the input argument are located. Once all such heap variables are identified, HEAP_FREE releases them in a final pass. Pointers are released as if the PTR_FREE procedure was called. Objects are released as with a call to OBJ_DESTROY.

HEAP_FREE is recommended when:

  • The data structures involved are highly complex, nested, or variable, and writing cleanup code is difficult and error prone.
  • The data structures are opaque, and the code cleaning up does not have knowledge of the structure.

See HEAP_FREEfor further details.



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