NAG Fortran Compiler, Release 7.2: f90_preconn_io

Navigation: Previous Up Next

## 6.5 f90_preconn_io

This module enables alteration of the default values used by automatically preconnected files.

### 6.5.1 Procedures

Note that in the descriptions below, `LOGICAL(*)` means any kind of `LOGICAL`. Also, note that although the `VERBOSE` argument is an optional argument, the actual argument is not permitted to be a non-present optional dummy argument.

    SUBROUTINE GET_PCIO_OPTIONS(BLANK,POSITION,PREFIX,VERBOSE)
    CHARACTER(*),OPTIONAL,INTENT(OUT) :: BLANK,POSITION,PREFIX
    LOGICAL(*),OPTIONAL,INTENT(OUT) :: VERBOSE

Returns the current settings for file preconnection; the meanings for these settings are described under the `IOINIT` routine. Both the `BLANK` and `POSITION` values are returned in upper case, even if lower case was used in a call to `IOINIT` to set them.

    SUBROUTINE IOINIT(BLANK,POSITION,PREFIX,VERBOSE)
    CHARACTER(*),OPTIONAL,INTENT(IN) :: BLANK,POSITION,PREFIX
    LOGICAL(*),OPTIONAL,INTENT(IN) :: VERBOSE

This procedure controls automatic file preconnection. Files can be automatically preconnected when a logical unit is initially referenced without an OPEN statement; preconnection does not occur again after file CLOSE.

The name of the file to be preconnected is determined first by searching for an environment variable of the form `FORT`nn where nn is the two-digit logical unit number; e.g. `FORT03`. If this environment variable is found its value is used as the filename; otherwise the name “`fort.`n” is used; e.g. ‘`fort.3`’. The file is opened either with `FORM='FORMATTED'` or `FORM='UNFORMATTED'` depending on whether the initial reference is with a formatted or unformatted i/o statement.

The `BLANK` and `POSITION` arguments control the `BLANK=` and `POSITION=` keywords in the implied `OPEN` statement when the file is preconnected; initially these are set to `BLANK='NULL'` and `POSITION='REWIND'`. Note that these have no meaning (and no effect) for unformatted files.

The `PREFIX` argument changes the prefix used to find the environment variable containing the preconnected file name. Initially this is ‘`FORT`’. Only the first 30 characters of `PREFIX` are used.

The `VERBOSE` argument controls activity reporting; if it is `.TRUE.`, subsequent preconnection activity will produce informative messages on the standard error unit.

### 6.5.2 Example

       USE F90_PRECONN_IO
       CALL IOINIT(BLANK='ZERO',PREFIX='MYFILE')
       READ (99,10) I,J,K,L,M
    10 FORMAT(I3,I1,I3,I1,I3)

When the READ statement is executed, the environment variable `MYFILE99` is interrogated to discover which file is to be automatically preconnected to unit 99. The unit will be connected with `BLANK='ZERO'`. If no environment variable is found the file ‘`fort.99`’ will be opened.