nextblock

Information on next block in blocked file-set

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Syntax

blkInfo = nextblock(bs)

Description

blkInfo = nextblock(bs) returns the information on the next block in the BlockedFileSet object bs, then advances the internal pointer of the blocked file-set to the next block. Subsequent calls to the nextblock function continue reading from the endpoint of the previous call.

example

Examples

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Open Live Script

Check if a blocked file-set has another block available to process and read the data iteratively.

Create a blocked file-set bs for a collection of files.

folder = {'accidents.mat','airlineResults.mat','census.mat','earth.mat'}
folder = 1×4 cell
    {'accidents.mat'}    {'airlineResults.mat'}    {'census.mat'}    {'earth.mat'}


bs = matlab.io.datastore.BlockedFileSet(folder)
bs = 
  BlockedFileSet with properties:

                   NumBlocks: 4
               NumBlocksRead: 0
                   BlockSize: 'file'
                   BlockInfo: Show BlockInfo for all 4 blocks
    AlternateFileSystemRoots: {}

Use the hasNextBlock and nextblock functions to read block information one block at a time while blocks remain in the set.

while hasNextBlock(bs)
   file = nextblock(bs)
end
file = 
  1×1 BlockInfo
                                                        Filename                                                         FileSize    Offset    BlockSize
    _________________________________________________________________________________________________________________    ________    ______    _________

    "/mathworks/devel/bat/filer/batfs2566-0/Bdoc25b.2988451/build/runnable/matlab/toolbox/matlab/demos/accidents.mat"      7343        0         7343   


file = 
  1×1 BlockInfo
                                       Filename                                        FileSize     Offset    BlockSize 
    ______________________________________________________________________________    __________    ______    __________

    "/tmp/Bdoc25b_2988451_1242027/tp0f1832b3/matlab-ex12893120/airlineResults.mat"    1.5042e+05      0       1.5042e+05


file = 
  1×1 BlockInfo
                                                       Filename                                                       FileSize    Offset    BlockSize
    ______________________________________________________________________________________________________________    ________    ______    _________

    "/mathworks/devel/bat/filer/batfs2566-0/Bdoc25b.2988451/build/runnable/matlab/toolbox/matlab/demos/census.mat"      353         0          353   


file = 
  1×1 BlockInfo
                                                      Filename                                                       FileSize    Offset    BlockSize
    _____________________________________________________________________________________________________________    ________    ______    _________

    "/mathworks/devel/bat/filer/batfs2566-0/Bdoc25b.2988451/build/runnable/matlab/toolbox/matlab/demos/earth.mat"     32522        0         32522  


Input Arguments
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Blocked file-set, specified as a matlab.io.datastore.BlockedFileSet object. To create a BlockedFileSet object, see matlab.io.datastore.BlockedFileSet.
Example: nextblock(bs)
Output Arguments
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This property is read-only.
Information about blocks in the BlockedFileSet object, returned
            as a BlockInfo object with the following properties:


  • Filename — Name of the file in the
                    BlockedFileSet object. The name contains the full path of the
                  file.
  • FileSize — Size of the file in number of bytes. 
  • Offset — Starting offset within the file to be read.
  • BlockSize — Size of the block in number of bytes.


Tips
  • The nextblock function returns an error if no more blocks exist in
          the BlockedFileSet object. To avoid this error, use
            nextblock along with hasNextBlock and
            reset. The hasNextBlock function checks if blocks
          still remain in the blocked file-set, while the reset method resets the
          internal pointer to the beginning of the blocked file-set.
Version History
Introduced in R2020a
See Also