Methods of Handling Errors

Whenever possible, the Intel® Fortran RTL does certain error handling, such as generating appropriate messages and taking necessary action to recover from errors. You can explicitly supplement or override default actions by using the following methods:

Use the END, EOR, and ERR Branch Specifiers

When a severe error occurs during Intel® Fortran program execution, the default action is to display an error message and terminate the program. To override this default action, there are three branch specifiers you can use in I/O statements to transfer control to a specified point in the program:

If you use the END, EOR, or ERR branch specifiers, no error message is displayed and execution continues at the designated statement, usually error-handling code.

You might encounter an unexpected error that the error-handling routine cannot handle. In this case, do one of the following:

After you modify the source code, compile, link, and run the program to display the error message. For example:

    READ (8,50,ERR=400)

If any severe error occurs during execution of this statement, the Intel® Visual Fortran RTL transfers control to the statement at label 400. Similarly, you can use the END specifier to handle an end-of-file condition that might otherwise be treated as an error. For example:

    READ (12,70,END=550)

When using non-advancing I/O, use the EOR specifier to handle the end-of-record condition. For example:

150 FORMAT (F10.2, F10.2, I6)
    READ (UNIT=20, FMT=150, SIZE=X, ADVANCE='NO', EOR=700) A, F, I

You can also use ERR as a specifier in an OPEN, CLOSE, or INQUIRE statement. For example:

    OPEN (UNIT=10, FILE='FILNAME', STATUS='OLD', ERR=999)

If an error is detected during execution of this OPEN statement, control transfers to the statement at label 999.

Use the IOSTAT Specifier and Fortran Exit Codes

The IOSTAT specifier can be used to continue program execution after an I/O error, or an end-of-file or end-of-record condition occurs, and to return information about the status of I/O operations. Certain error conditions are not returned in IOSTAT.

The IOSTAT specifier can supplement or replace the use of the END=, EOR=, and ERR= branch specifiers.

Use of an IOSTAT= specifier in an I/O statement prevents initiation of error termination if an error occurs during the execution of the I/O statement. The integer variable specified in the IOSTAT= specifier becomes defined during the execution of the I/O statement with the following values:

Note that the value assigned to the IOSTAT variable is the same value that would be returned as an exit code if error termination was initiated.

Following the execution of the I/O statement and assignment of an IOSTAT value, control transfers to the END=, EOR=, or ERR= statement label, if any. If there is no control transfer, normal execution continues.

The non-standard include file FOR_ISODEF.FOR and the non-standard module FORISODEF contain symbolic constants for the values returned through an IOSTAT= specifier.

The following example uses the IOSTAT specifier and the module FORIOSDEF to handle an OPEN statement error (in the FILE specifier).


     USE foriosdef
     IMPLICIT NONE
     CHARACTER(LEN=40) :: FILNM
     INTEGER IERR
     PRINT *, 'Type file name:'
     READ (*,*) FILNM
     OPEN (UNIT=1, FILE=FILNM, STATUS='OLD', IOSTAT=IERR, ERR=100)
     PRINT *, 'Opening file: ', FILNM
     ! process the input file
     ...
     CLOSE (UNIT=1)
     STOP
 100 IF(IERR . EQ. FOR$IOS_FILNOTFOU) THEN
        PRINT *, 'File: ', FILNM, ' does not exist '
     ELSE 
        PRINT *, 'Unrecoverable error, code =', IERR
     END IF
     END PROGRAM

Another way to obtain information about an error is by using the ERRSNS subroutine, which allows you to obtain the last I/O system error code associated with an Intel® Fortran RTL error.

See Also