@node Obstacks
-@chapter Obstacks
+@subsection Obstacks
@cindex obstacks
An @dfn{obstack} is a pool of memory containing a stack of objects. You
the padding needed to start each object on a suitable boundary.
@menu
-* Creating Obstacks:: How to declare an obstack in your program.
-* Preparing for Obstacks:: Preparations needed before you can
- use obstacks.
+* Creating Obstacks:: How to declare an obstack in your program.
+* Preparing for Obstacks:: Preparations needed before you can
+ use obstacks.
* Allocation in an Obstack:: Allocating objects in an obstack.
* Freeing Obstack Objects:: Freeing objects in an obstack.
-* Obstack Functions:: The obstack functions are both
- functions and macros.
+* Obstack Functions:: The obstack functions are both
+ functions and macros.
* Growing Objects:: Making an object bigger by stages.
-* Extra Fast Growing:: Extra-high-efficiency (though more
- complicated) growing objects.
+* Extra Fast Growing:: Extra-high-efficiency (though more
+ complicated) growing objects.
* Status of an Obstack:: Inquiries about the status of an obstack.
* Obstacks Data Alignment:: Controlling alignment of objects in obstacks.
* Obstack Chunks:: How obstacks obtain and release chunks;
- efficiency considerations.
+ efficiency considerations.
* Summary of Obstacks::
@end menu
@node Creating Obstacks
-@section Creating Obstacks
+@subsubsection Creating Obstacks
The utilities for manipulating obstacks are declared in the header
file @file{obstack.h}.
These matters are described in the following section.
@node Preparing for Obstacks
-@section Preparing for Using Obstacks
+@subsubsection Preparing for Using Obstacks
Each source file in which you plan to use the obstack functions
must include the header file @file{obstack.h}, like this:
@end defvar
@node Allocation in an Obstack
-@section Allocation in an Obstack
+@subsubsection Allocation in an Obstack
@cindex allocation (obstacks)
The most direct way to allocate an object in an obstack is with
@code{malloc} (@pxref{Basic Allocation, , , libc, The GNU C Library Reference Manual}).
@node Freeing Obstack Objects
-@section Freeing Objects in an Obstack
+@subsubsection Freeing Objects in an Obstack
@cindex freeing (obstacks)
To free an object allocated in an obstack, use the function
obstacks, or non-obstack allocation, can reuse the space of the chunk.
@node Obstack Functions
-@section Obstack Functions and Macros
+@subsubsection Obstack Functions and Macros
@cindex macros
The interfaces for using obstacks may be defined either as functions or
compute each argument only once.
@node Growing Objects
-@section Growing Objects
+@subsubsection Growing Objects
@cindex growing objects (in obstacks)
@cindex changing the size of a block (obstacks)
length---there's no telling what will happen if you do that.
@node Extra Fast Growing
-@section Extra Fast Growing Objects
+@subsubsection Extra Fast Growing Objects
@cindex efficiency and obstacks
The usual functions for growing objects incur overhead for checking
@end smallexample
@node Status of an Obstack
-@section Status of an Obstack
+@subsubsection Status of an Obstack
@cindex obstack status
@cindex status of obstack
@end deftypefun
@node Obstacks Data Alignment
-@section Alignment of Data in Obstacks
+@subsubsection Alignment of Data in Obstacks
@cindex alignment (in obstacks)
Each obstack has an @dfn{alignment boundary}; each object allocated in
the obstack automatically starts on an address that is a multiple of the
-specified boundary. By default, this boundary is 4 bytes.
+specified boundary. By default, this boundary is aligned so that
+the object can hold any type of data.
To access an obstack's alignment boundary, use the macro
@code{obstack_alignment_mask}, whose function prototype looks like
The value is a bit mask; a bit that is 1 indicates that the corresponding
bit in the address of an object should be 0. The mask value should be one
less than a power of 2; the effect is that all object addresses are
-multiples of that power of 2. The default value of the mask is 3, so that
+multiples of that power of 2. The default value of the mask is a value
+that allows aligned objects to hold any type of data: for example, if
+its value is 3, any type of data can be stored at locations whose
addresses are multiples of 4. A mask value of 0 means an object can start
on any multiple of 1 (that is, no alignment is required).
the next object.
@node Obstack Chunks
-@section Obstack Chunks
+@subsubsection Obstack Chunks
@cindex efficiency of chunks
@cindex chunks
@end smallexample
@node Summary of Obstacks
-@section Summary of Obstack Functions
+@subsubsection Summary of Obstack Functions
Here is a summary of all the functions associated with obstacks. Each
takes the address of an obstack (@code{struct obstack *}) as its first