07-16-2009
A method is like a subroutine. An example might be a file of dictionary words. Instead of writing. you "insert" the word. Somehow the system keeps the words in alphabetical order. You can retrieve a list of all word in alphabetical order or you can search for a word. But the data file itself is a black box and you can't access it. If you put 1,234 bytes worth of words into the data file it will be bigger than 1,234 bytes. The system needs some extra stuff to find it's way around the file. This extra stuff is the control blocks.
And believe it or not, there used to be a sequential file which behaved like a really stupid tape drive. You could read it. You could even read it byte-by-byte. But after you read, say, byte number 123, you had two choices: read byte 124 or close the file. However, the OS could predict a program's behavior rather easily and this was fast (for it's day).
There might be a "random" file where you could seek and then read, but it was slow. After seeking to byte 123 and reading one byte, you could next seek to byte 124 and read that. But if you wanted a sequential file, you were supposed use a sequential file, not a random file.
Mind you, a single data file might be opened as "sequential" by one program and "random" by another. But then each program had a different interface (or subroutine or method) to read the file. However there was no way to execute a data file or to read a program file.
There were many file types and OS's competed by offering more file types. The Unix model of just one file type displaced all of this.
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LEARN ABOUT DEBIAN
tiffreadscanline
TIFFReadScanline(3TIFF) TIFFReadScanline(3TIFF)
NAME
TIFFReadScanline - read and decode a scanline of data from an open TIFF file
SYNOPSIS
#include <tiffio.h>
int TIFFReadScanline(TIFF *tif, tdata_t buf, uint32 row, tsample_t sample)
DESCRIPTION
Read the data for the specified row into the (user supplied) data buffer buf. The data are returned decompressed and, in the native byte-
and bit-ordering, but are otherwise packed (see further below). The buffer must be large enough to hold an entire scanline of data. Appli-
cations should call the routine TIFFScanlineSize to find out the size (in bytes) of a scanline buffer. The row parameter is always used by
TIFFReadScanline; the sample parameter is used only if data are organized in separate planes (PlanarConfiguration=2).
NOTES
The library attempts to hide bit- and byte-ordering differences between the image and the native machine by converting data to the native
machine order. Bit reversal is done if the FillOrder tag is opposite to the native machine bit order. 16- and 32-bit samples are automati-
cally byte-swapped if the file was written with a byte order opposite to the native machine byte order,
In C++ the sample parameter defaults to 0.
RETURN VALUES
TIFFReadScanline returns -1 if it detects an error; otherwise 1 is returned.
DIAGNOSTICS
All error messages are directed to the TIFFError(3TIFF) routine.
Compression algorithm does not support random access. Data was requested in a non-sequential order from a file that uses a compression
algorithm and that has RowsPerStrip greater than one. That is, data in the image is stored in a compressed form, and with multiple rows
packed into a strip. In this case, the library does not support random access to the data. The data should either be accessed sequentially,
or the file should be converted so that each strip is made up of one row of data.
BUGS
Reading subsampled YCbCR data does not work correctly because, for PlanarConfiguration=2 the size of a scanline is not calculated on a per-
sample basis, and for PlanarConfiguration=1 the library does not unpack the block-interleaved samples; use the strip- and tile-based inter-
faces to read these formats.
SEE ALSO
TIFFOpen(3TIFF), TIFFReadEncodedStrip(3TIFF), TIFFReadRawStrip(3TIFF), libtiff(3TIFF)
Libtiff library home page: http://www.remotesensing.org/libtiff/
libtiff October 15, 1995 TIFFReadScanline(3TIFF)