nextblock

Information on next block in blocked file-set

Since R2020a

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.

Examples

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Check If Blocked File-Set Has Another Block

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 = 1x4 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: 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 = 
  1x1 BlockInfo
                                                    Filename                                                    FileSize    Offset    BlockSize
    ________________________________________________________________________________________________________    ________    ______    _________

    "/mathworks/devel/bat/filer/batfs1904-0/Bdoc24a.2528353/build/matlab/toolbox/matlab/demos/accidents.mat"      7343        0         7343

file = 
  1x1 BlockInfo
                                      Filename                                        FileSize     Offset    BlockSize 
    _____________________________________________________________________________    __________    ______    __________

    "/tmp/Bdoc24a_2528353_989294/tpe9f9016d/matlab-ex12893120/airlineResults.mat"    1.5042e+05      0       1.5042e+05

file = 
  1x1 BlockInfo
                                                  Filename                                                   FileSize    Offset    BlockSize
    _____________________________________________________________________________________________________    ________    ______    _________

    "/mathworks/devel/bat/filer/batfs1904-0/Bdoc24a.2528353/build/matlab/toolbox/matlab/demos/census.mat"      353         0          353

file = 
  1x1 BlockInfo
                                                  Filename                                                  FileSize    Offset    BlockSize
    ____________________________________________________________________________________________________    ________    ______    _________

    "/mathworks/devel/bat/filer/batfs1904-0/Bdoc24a.2528353/build/matlab/toolbox/matlab/demos/earth.mat"     32522        0         32522

Input Arguments

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`bs` — Blocked file-set
`matlab.io.datastore.BlockedFileSet` object

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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`blkInfo` — Information about blocks
`BlockInfo` object

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.