HP Fortran Programmer's Reference (September 2007)

I/O runtime error messages
Appendix A660
INTEGER ios
.
.
.
OPEN (10, FILE='data_file', ERR=99, IOSTAT=ios)
If data_file is successfully opened, ios will return 0; if for any reason the file cannot be
opened, a nonzero status code will be returned in ios. By referring to this appendix, you can
get information about the error and how to correct it.