Help Files: Fortran77: Error Messages
HELP June 15, 1985 F77/ERROR_MSGS
Interpreting Execution Error Messages
1. Types of Errors
Execution error messages for Fortran programs are generated by
the Fortran I/O library (error number = -1 or > 99), by the UNIX
system routines ( 0 < error number < 99), and by the UNIX signal
handler (no error number printed).
2. Fortran I/O Library Error Messages
Here are examples of two common I/O errors; for a complete list
of the Fortran I/O library error messages, see "help f77
io_err_msgs". The first error results from trying to read beyond
the end of a file:
dofio: [-1] end of file
logical unit 5, named 'stdin'
lately: reading sequential formatted external I/O
format: (i10)
*** Execution terminated
The first line names the system routine, dofio(), that issued the
error message, gives the error message number, -1, and a short
description of the error. The second line shows that the error
involved Fortran logical unit 5 and file 'stdin' (standard in-
put). The third line tells the type of I/O being attempted.
The second example is a little more complex:
dofio: [115] invalid data for integer format term
logical unit 5, named 'stdin'
lately: reading sequential formatted external I/O
format: (i10)
part of last data: 22|e8
*** Execution terminated
The program tried to read ``22e8'' with an ``i5'' format term.
The I/O library is complaining that the letter ``e'' is not a
valid input character when reading integers. There is a new
line, listing the data being read, which was not present in the
previous error message. A vertical bar, ``|'', is put next to
the input character the formatting routines were scanning when
the error was detected. This line is only generated when doing
I/O with disk files. In this example, the program was invoked
by:
a.out < data
The program is reading a disk file via the redirection of stan-
dard input.
Any error detected during I/O processing will cause the program
to abort unless the I/O statement included an 'err=' clause to
provide a branch on error or an 'iostat=' clause to save the er-
ror code. Read statements may include 'end=' to branch on end-
of-file.
3. Signal Handler Error Messages
Most arithmetic errors and other errors causing hardware inter-
rupts cause a signal to be sent to the process that caused the
error. If, as is typical with Fortran programs, the process has
not been set up to handle signals, then the process is terminated
with an appropriate (although sometimes mysterious) error mes-
sage. These error messages usually appear with no numbers; how-
ever under certain circumstances, the error numbers may also ap-
pear.
The most common of these messages are reproduced and explained
here:
*** Arithmetic Exception: Floating point overflow
*** Execution Terminated
The program tried to generate a floating point number greater in
absolute value than approximately 1.7e+38.
*** Arithmetic Exception: Integer divide by 0
*** Execution Terminated
The program divided by an integer zero; this is mathematically
undefined.
*** Arithmetic Exception: Floating divide by zero
*** Execution Terminated
The program divided by a floating point zero; this is mathemati-
cally undefined.
*** Arithmetic Exception: Integer overflow
*** Execution Terminated
The program tried to generate an integer outside the VAX's range
of integers, either greater than 2**31-1 (2147483647) or less
than -2**31 (-2147483648). This interrupt is not normally en-
abled; to catch this error, you need to call subroutine traper()
in each subprogram (see "man 3f traper").
*** Arithmetic Exception: Floating point underflow
*** Execution Terminated
The program tried to generate a floating point number whose abso-
lute value is less than 2.9e-39. This trap is not normally en-
abled; to enable it you must call subroutine traper() in each
subprogram (see "man 3f traper").
*** Segmentation violation
*** Execution Terminated
The program tried to reference beyond the current bounds of its
memory. This is usually caused by using invalid subscripts for
an array; recompiling and rerunning with the ``-C'' flag will
catch many of these errors.
*** Bus error
*** Execution Terminated
The program has tried to store in a protected area such as the
code for the program. This is often caused by using an invalid
subscript when storing into an array; recompiling and rerunning
with the ``-C'' option will find many of these errors. This may
also be caused by calling a subprogram passing fewer actual argu-
ments than are declared and used in the subprogram. It can also
occur when a subroutine or function is passed as an argument to a
subprogram when the subprogram is expecting a variable or array
and the subprogram tries to store in the argument. Storing on
top of a constant, e.g.:
call sub(0)
...
subroutine sub(ival)
ival = min0(ival,3000)
also causes this error.
*** Illegal instruction
*** Execution Terminated
This may mean that your program is overwriting itself. This is
uncommon because the program code and variable storage are in
different areas of memory and the program code is normally pro-
tected.
*** Illegal operand
*** Execution Terminated
An invalid floating point number (exponent value of 0, sign value
of 1) was used in a floating point computation. This is a
reserved operand in the floating point logic of the VAX. If an
integer multiple of 32768 is used as a real, this interrupt will
be generated.
For a complete list of signals, see "man 2 sigvec" or "man 3c
signal".
The user can regain control after signal handler errors via the
signal() subroutine (see "man 3f signal"). Unfortunately, after
regaining control, there is currently no way to resume exactly
where you left off.
4. Errors due to unsuccessful system calls
This type of message is less common than the other two types.
Here are two examples. The following messages result from trying
to read from a file for which you do not have read permission:
fort.1: [13] Permission denied
logical unit 1, named 'fort.1'
*** Execution Terminated
and the following resulted when trying to read from unit 6, stan-
dard output:
read sfe: [9] Bad file number
logical unit 6, named 'stdout'
lately: reading sequential formatted external IO
format: (i5)
*** Execution Terminated
Unfortunately, these errors are numbered using the same number
range as the signal errors described above. For example, an er-
ror 24 could either be the system call error 24, too many files
open, or signal message 24, cpu time limit exceeded. The context
usually makes it clear which type of error has occurred; also the
signal messages normally appear without numbers.
Comments to decf@euler.berkeley.edu
© 1998 UC Regents