x04acf is especially useful if the calling language is not Fortran. It opens a Fortran unit number for reading, writing or appending, and associates the unit with a filename specified by the argument file.

4 References

None.

5 Arguments

1: $iounit$ – Integer Input

On entry: the Fortran unit number which identifies the file to be read from, written to or appended to. Note that this may be system dependent. Values in the range

7

1000

should however be safe on most systems.

2: $file$ – Character(*) Input

On entry: the name of the file to be opened.

Constraint: must contain a valid filename for the computer system being used.

3: $mode$ – Integer Input

On entry: specifies whether the file is to be opened for reading, writing or appending.

$mode = 0$: The file is to be opened for reading.
$mode = 1$: The file is to be opened for writing.
$mode = 2$: The file is to be opened for appending.

Constraint:

0 \leq mode \leq 2

4: $ifail$ – Integer Input/Output

On entry: ifail must be set to

0

−1

1

to set behaviour on detection of an error; these values have no effect when no error is detected.

A value of

0

causes the printing of an error message and program execution will be halted; otherwise program execution continues. A value of

−1

means that an error message is printed while a value of

1

means that it is not.

If halting is not appropriate, the value

−1

1

is recommended. If message printing is undesirable, then the value

1

is recommended. Otherwise, the value

0

is recommended. When the value $- 1$ or $1$ is used it is essential to test the value of ifail on exit.

On exit:

ifail = 0

unless the routine detects an error or a warning has been flagged (see Section 6).

6 Error Indicators and Warnings

If on entry

ifail = 0

−1

, explanatory error messages are output on the current error message unit (as defined by x04aaf).

Errors or warnings detected by the routine:

$ifail = 1$: On entry, $mode = ⟨ value ⟩$ .
Constraint: $0 \leq mode \leq 2$ .

$ifail = 2$: Cannot open file $⟨ value ⟩$ for reading on channel $⟨ value ⟩$ .

$ifail = 3$: Cannot open file $⟨ value ⟩$ for writing on channel $⟨ value ⟩$ .

$ifail = 4$: Cannot open file $⟨ value ⟩$ for appending on channel $⟨ value ⟩$ .

$ifail = - 99$: An unexpected error has been triggered by this routine. Please contact NAG.
See Section 7 in the Introduction to the NAG Library FL Interface for further information.

$ifail = - 399$: Your licence key may have expired or may not have been installed correctly.
See Section 8 in the Introduction to the NAG Library FL Interface for further information.