HP Fortran Programmer's Guide (B3908-90031; September 2011)

Using the ON statement
Exceptions handled by the ON statement
Chapter 5 131
Exceptions handled by the ON statement
Like the +fp_exception option, the ON statement enables traps for floating-point exceptions (by default,
traps for floating-point exceptions are disabled on HP 9000 computers). When traps are enabled, an
executing program that takes any of the following exceptions will abort, unless an ON statement specifies a
different action:
• Division by zero
• Overflow
• Underflow
• Inexact result
• Invalid (or illegal) operation
These exceptions are defined by the IEEE standard for floating-point operations. The ON statement enables
traps for these exceptions, regardless of whether the exception is taken by user code or by a call to a library
routine. In addition, the ON statement also enables traps for integer division by zero, integer overflow, and
+Ctrl-C interrupts. The +Ctrl-C interrupt occurs when the user presses +Ctrl-C during program execution.
Table 5-1 on page 131 lists the exceptions handled by the ON statement and gives the keywords that must be
specified in the ON statement to indicate the exception being handled. The first column indicates the type of
exception. The second column gives the keywords that must appear in the ON statement, immediately
following the word ON. The third column gives alternate keywords you can specify instead of those in the
second column.
For example, the following ON statement will trap attempts to divide by zero with 8-byte floating-point
operands:
ON REAL(8) DIV 0 CALL div_zero_trap
The next example ON statement does the same as the first but uses the alternate keywords from the third
column of the table:
ON DOUBLE PRECISION DIV 0 CALL div_zero_trap
Table 5-1 Exceptions handled by the ON statement
Exceptions Exception keywords Alternate keywords
Division by zero REAL(4) DIV 0 REAL DIV 0
REAL(8) DIV 0 DOUBLE PRECISION DIV 0
REAL(16) DIV 0 (none)