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READ Statement question

 
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mike.smartcam



Joined: 02 Aug 2014
Posts: 40
Location: Lancashire, United Kingdom
PostPosted: Mon Jan 19, 2015 7:52 pm    Post subject: READ Statement question Reply with quote
Hi Group,

The following code is designed to read data from a file:

Code:
* FILE: READ_ID.FOR
* SUBROUTINE TO READ FIRST TO RECORD OF A FILE
***********************************************************************
      SUBROUTINE READ_ID(UNIT,NUM,ERROR)
      IMPLICIT NONE
      INTEGER NUM,UNIT
      CHARACTER *60 STRING
      LOGICAL ERROR

      ERROR = .FALSE.
      READ(UNIT,'(A)',ERR=99)STRING
      READ(UNIT,*,ERR=99)NUM

      RETURN
99    PRINT*,'ERROR in reading file header.'
      ERROR = .TRUE.
      RETURN
      END


Can anyone tell me please what is the purpose of '(A)' in the following code line:

Code:
READ(UNIT,'(A)',ERR=99)STRING


Thanks for any comments.
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Mike
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davidb



Joined: 17 Jul 2009
Posts: 560
Location: UK
PostPosted: Mon Jan 19, 2015 8:43 pm    Post subject: Reply with quote
Code:

READ(UNIT,'(A)',ERR=99)STRING


means the same as
Code:

READ(UNIT,10,ERR=99)STRING
10 FORMAT(A)


The format specifier A means read a string of 60 characters then advance to the next record. It is 60 because the variable STRING is of length 60.

If you just want to skip read a record, as in your code STRING isn't actually used, you can use an empty format specifier and no data items, like this:

Code:

READ(UNIT,'()',ERR=99)

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Last edited by davidb on Mon Jan 19, 2015 8:50 pm; edited 1 time in total
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mecej4



Joined: 31 Oct 2006
Posts: 1886
PostPosted: Mon Jan 19, 2015 8:50 pm    Post subject: Reply with quote
You can read string variables using a list directed input statement, instead of using the A format specifier. However, if the input line contains one or more blanks, the string read ends at the first blank even if the string variable can hold more. For example, if the input line is 'Setting Environment' and the character variable has size 30, reading with list-directed I/O gives 'Setting' whereas the A format gives the entire input string.
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mike.smartcam



Joined: 02 Aug 2014
Posts: 40
Location: Lancashire, United Kingdom
PostPosted: Tue Jan 27, 2015 4:13 pm    Post subject: Reply with quote
Thank you for the clarification.
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Mike
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