NAG Library Routine Document

X04ACF

1  Purpose

2  Specification

3  Description

4  References

5  Parameters

1:     IOUNIT – INTEGERInput

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 $7$ to $1000$ 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 – INTEGERInput

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

$\mathbf{MODE}=0$

The file is to be opened for reading.

$\mathbf{MODE}=1$

The file is to be opened for writing.

$\mathbf{MODE}=2$

The file is to be opened for appending.

Constraint: $0\le \mathbf{MODE}\le 2$.

4:     IFAIL – INTEGERInput/Output

On entry: IFAIL must be set to $0$, $-1\text{ or }1$. If you are unfamiliar with this parameter you should refer to Section 3.3 in the Essential Introduction for details.

For environments where it might be inappropriate to halt program execution when an error is detected, the value $-1\text{ or }1$ is recommended. If the output of error messages is undesirable, then the value $1$ is recommended. Otherwise, if you are not familiar with this parameter, the recommended value is $0$. When the value $-\mathbf{1}\text{ or }\mathbf{1}$ is used it is essential to test the value of IFAIL on exit.

On exit: $\mathbf{IFAIL}=\mathbf{0}$ unless the routine detects an error or a warning has been flagged (see Section 6).

6  Error Indicators and Warnings

$\mathbf{IFAIL}=1$

On entry, MODE is invalid.

$\mathbf{IFAIL}=2$

Failure to open the file for reading.

$\mathbf{IFAIL}=3$

Failure to open the file for writing.

$\mathbf{IFAIL}=4$

Failure to open the file for appending.

7  Accuracy

8  Further Comments

9  Example

9.1  Program Text

Program Text (x04acfe.f90)

9.2  Program Data

9.3  Program Results

Program Results (x04acfe.r)