NAME
Image::Leptonica::Func::bbuffer
VERSION
version 0.04
bbuffer.c
bbuffer.c
Create/Destroy BBuffer
BBUFFER *bbufferCreate()
void *bbufferDestroy()
l_uint8 *bbufferDestroyAndSaveData()
Operations to read data TO a BBuffer
l_int32 bbufferRead()
l_int32 bbufferReadStream()
static l_int32 bbufferExtendArray()
Operations to write data FROM a BBuffer
l_int32 bbufferWrite()
l_int32 bbufferWriteStream()
Accessors
l_int32 bbufferBytesToWrite()
Read from stdin to memory
l_int32 bbufferReadStdin()
The bbuffer is an implementation of a byte queue.
The bbuffer holds a byte array from which bytes are
processed in a first-in/first-out fashion. As with
any queue, bbuffer maintains two "pointers," one to the
tail of the queue (where you read new bytes onto it)
and one to the head of the queue (where you start from
when writing bytes out of it.
The queue can be visualized:
byte 0 byte (nalloc - 1)
| |
--------------------------------------------------
H T
[ aw ][ bytes currently on queue ][ anr ]
---: all allocated data in bbuffer
H: queue head (ptr to next byte to be written out)
T: queue tail (ptr to first byte to be written to)
aw: already written from queue
anr: allocated but not yet read to
The purpose of bbuffer is to allow you to safely read
bytes in, and to sequentially write them out as well.
In the process of writing bytes out, you don't actually
remove the bytes in the array; you just move the pointer
(nwritten) which points to the head of the queue. In
the process of reading bytes in, you sometimes need to
expand the array size. If a read is performed after a
write, so that the head of the queue is not at the
beginning of the array, the bytes already written are
first removed by copying the others over them; then the
new bytes are read onto the tail of the queue.
Note that the meaning of "read into" and "write from"
the bbuffer is OPPOSITE to that for a stream, where
you read "from" a stream and write "into" a stream.
As a mnemonic for remembering the direction:
- to read bytes from a stream into the bbuffer,
you call fread on the stream
- to write bytes from the bbuffer into a stream,
you call fwrite on the stream
See zlibmem.c for an example use of bbuffer, where we
compress and decompress an array of bytes in memory.
We can also use the bbuffer trivially to read from stdin
into memory; e.g., to capture bytes piped from the stdout
of another program. This is equivalent to repeatedly
calling bbufferReadStream() until the input queue is empty.FUNCTIONS
bbufferBytesToWrite
l_int32 bbufferBytesToWrite ( BBUFFER *bb, size_t *pnbytes )
bbufferBytesToWrite()
Input: bbuffer
&nbytes (<return>)
Return: 0 if OK; 1 on errorbbufferCreate
BBUFFER * bbufferCreate ( l_uint8 *indata, l_int32 nalloc )
bbufferCreate()
Input: buffer address in memory (<optional>)
size of byte array to be alloc'd (0 for default)
Return: bbuffer, or null on error
Notes:
(1) If a buffer address is given, you should read all the data in.
(2) Allocates a bbuffer with associated byte array of
the given size. If a buffer address is given,
it then reads the number of bytes into the byte array.bbufferDestroy
void bbufferDestroy ( BBUFFER **pbb )
bbufferDestroy()
Input: &bbuffer (<to be nulled>)
Return: void
Notes:
(1) Destroys the byte array in the bbuffer and then the bbuffer;
then nulls the contents of the input ptr.bbufferDestroyAndSaveData
l_uint8 * bbufferDestroyAndSaveData ( BBUFFER **pbb, size_t *pnbytes )
bbufferDestroyAndSaveData()
Input: &bbuffer (<to be nulled>)
&nbytes (<return> number of bytes saved in array)
Return: barray (newly allocated array of data)
Notes:
(1) Copies data to newly allocated array; then destroys the bbuffer.bbufferRead
l_int32 bbufferRead ( BBUFFER *bb, l_uint8 *src, l_int32 nbytes )
bbufferRead()
Input: bbuffer
src (source memory buffer from which bytes are read)
nbytes (bytes to be read)
Return: 0 if OK, 1 on error
Notes:
(1) For a read after write, first remove the written
bytes by shifting the unwritten bytes in the array,
then check if there is enough room to add the new bytes.
If not, realloc with bbufferExpandArray(), resulting
in a second writing of the unwritten bytes. While less
efficient, this is simpler than making a special case
of reallocNew().bbufferReadStdin
l_int32 bbufferReadStdin ( l_uint8 **pdata, size_t *pnbytes )
bbufferReadStdin()
Input: &data (<return> binary data read in)
&nbytes (<return>)
Return: 0 if OK; 1 on error
Notes:
(1) This can be used to capture data piped in from stdin.
For example, you can read an image from stdin into memory
using shell redirection, with one of these:
cat <imagefile> | readprog
readprog < <imagefile>
where readprog is:
bbufferReadStdin(&data, &nbytes); // l_uint8*, size_t
Pix *pix = pixReadMem(data, nbytes);bbufferReadStream
l_int32 bbufferReadStream ( BBUFFER *bb, FILE *fp, l_int32 nbytes )
bbufferReadStream()
Input: bbuffer
fp (source stream from which bytes are read)
nbytes (bytes to be read)
Return: 0 if OK, 1 on errorbbufferWrite
l_int32 bbufferWrite ( BBUFFER *bb, l_uint8 *dest, size_t nbytes, size_t *pnout )
bbufferWrite()
Input: bbuffer
dest (dest memory buffer to which bytes are written)
nbytes (bytes requested to be written)
&nout (<return> bytes actually written)
Return: 0 if OK, 1 on errorbbufferWriteStream
l_int32 bbufferWriteStream ( BBUFFER *bb, FILE *fp, size_t nbytes, size_t *pnout )
bbufferWriteStream()
Input: bbuffer
fp (dest stream to which bytes are written)
nbytes (bytes requested to be written)
&nout (<return> bytes actually written)
Return: 0 if OK, 1 on errorAUTHOR
Zakariyya Mughal <zmughal@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2014 by Zakariyya Mughal.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.