Microsoft KB Archive/68030

= FIX: Problem Reading Direct-Access File When RECL > BLOCKSIZE =

Article ID: 68030

Article Last Modified on 12/1/2003

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APPLIES TO


 * Microsoft FORTRAN Compiler 4.01
 * Microsoft FORTRAN Compiler 4.1
 * Microsoft FORTRAN Compiler 5.0
 * Microsoft FORTRAN Compiler 4.1
 * Microsoft FORTRAN Compiler 5.0

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This article was previously published under Q68030



SYMPTOMS
An application that reads records from a file produces incorrect results. This problem does not occur when the application is compiled with Microsoft FORTRAN versions 4.0 or 4.0a for MS-DOS.



CAUSE
The application opens a direct access file with BLOCKSIZE set to a value that is less than the RECL (record length).



RESOLUTION
Perform one of the following three methods to work around this problem:


 * Modify the source code to use a record length less than or equal to the BLOCKSIZE (the default BLOCKSIZE value is 1024 bytes).
 * Modify the source code to access the direct-access file with a variable or group of variables, the length of which in bytes matches the record length. This technique avoids partial record access.
 * Modify the source code to specify a REWIND statement following any partial access to a record. The REWIND statement realigns the file pointer to the beginning of the file. (The BACKSPACE statement does not appear to solve this problem.)



STATUS
Microsoft has confirmed this to be a problem in FORTRAN versions 4.01, 4.1, and 5.0 for MS-DOS and versions 4.1 and 5.0 for OS/2. This problem was corrected in FORTRAN version 5.1 for MS-DOS and OS/2.



MORE INFORMATION
The code sample below demonstrates this problem. The first DO-loop in the application constructs a direct-access scratch file that contains four records. Then the application performs a partial read of record 3 from the scratch file. Finally, a DO-loop reads the file from record 1 to record 4 and writes the results on the screen.

The program output indicates that the READ statement in the DO-loop improperly accesses the information in the scratch file. Because the RECL (record length) exceeds the BLOCKSIZE (buffer size), each READ statement causes the buffer to fill twice. Because the extra information is not flushed from the buffer, it is read into the ALINE variable each time the code executes a READ statement after the initial partial READ of record 3.

Sample Code
C Compile options needed: None

CHARACTER*514 ALINE CHARACTER*10 SHORT OPEN(9, ACCESS = 'DIRECT', RECL = 514,    + FORM = 'FORMATTED', BLOCKSIZE = 512) ! NOTE: BLOCKSIZE < RECL DO 10 J = 1, 4                       ! Create a file to read. ALINE = 'TEST ' // CHAR(#30 + J)  ! Put the record number WRITE(9, 30, REC = J) ALINE       ! into each record. 10   CONTINUE

READ(9, 30, REC = 3) SHORT  ! This is the partial READ ! of record 3. DO 20 I = 1, 4 READ(9, 30, REC = I) ALINE WRITE(*, *) ALINE 20   CONTINUE 30   FORMAT(A) END

Additional query words: 4.01 4.10 5.00 buglist4.01 buglist4.10 buglist5.00 fixlist5.10

Keywords: kbfix KB68030

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