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Variable Block file

 
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rajesh_mbt

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Joined: 27 Mar 2006
Posts: 95
Location: India

PostPosted: Wed Nov 26, 2008 3:22 pm    Post subject: Variable Block file
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Can any one clarify why we need to add 4 bytes with actual length for variable block file during submission of jcl?
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enrico-sorichetti

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Joined: 14 Mar 2007
Posts: 10210
Location: italy

PostPosted: Wed Nov 26, 2008 3:25 pm    Post subject: Reply to: Variable Block file
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how else would tell the block and record lengths
he VB layout is...
four bytes for the BDW bock descripotor word
followed by N tuples of
four bytes for the RDW record description word
the data itself

but anyway the practical reason is ... the manual says so
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Garry Carroll

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Joined: 08 May 2006
Posts: 991
Location: Dublin, Ireland / Edinburgh, Scotland

PostPosted: Wed Nov 26, 2008 3:27 pm    Post subject:
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The 4bytes contain the RDW (record descriptor word) which contains each individual record's length. Similarly, an additional 4 bytes are used to contain the size of the block containing the variable records.

Garry.
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Anuj Dhawan

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Joined: 22 Apr 2006
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Location: Mumbai, India

PostPosted: Thu Nov 27, 2008 12:06 am    Post subject:
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Hi,

A variable-length logical record consists of a 4-byte record descriptor word (RDW) followed by the data. The first 2 bytes contain the length of the logical record. The last 2 bytes must be 0 because these are used for spanned records. When using variable-length records on output, you must provide the RDW; for input, the operating system provides the RDW.

Click here, this link would give you a pictorial representation of what goes behind.
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Aaru

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Joined: 03 Jul 2007
Posts: 1288
Location: Chennai, India

PostPosted: Thu Nov 27, 2008 4:59 pm    Post subject: Reply to: Variable Block file
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Quote:
The first 2 bytes contain the length of the logical record. The last 2 bytes must be 0 because these are used for spanned records.


Adding to what Anuj had posted, last 2 bytes are populated with hexadecimal Zeroes.
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