C++ User's Guide

-`ftrap=`t

Sets the IEEE trapping mode in effect at start-up.

This option sets the IEEE 754 trapping modes that are established at program initialization, but does not install a SIGFPE handler. You can use ieee_handler to simultaneously enable traps and install a SIGFPE handler. When more than one value is used, the list is processed sequentially from left to right.

Values

t is a comma-separated list that consists of one or more of the following:

Value of `t`	Meaning
`[no%]division`	[Do not] Trap on division by zero.
`[no%]inexact`	[Do not] Trap on inexact result.
`[no%]invalid`	[Do not] Trap on invalid operation
`[no%]overflow`	[Do not] Trap on overflow.
`[no%]underflow`	[Do not] Trap on underflow.
`%all`	Trap on all of the above.
`%none`	Trap on none of the above.
`common`	Trap on invalid, division by zero, and overflow.

Note that the [no%] form of the option is used only to modify the meaning of the %all and common values, and must be used with one of these values, as shown in the example. The [no%] form of the option by itself does not explicitly cause a particular trap to be disabled.

If you wish to enable the IEEE traps, -ftrap=common is the recommended setting.

Defaults

If -ftrap is not specified, the -ftrap=%none value is assumed. (Traps are not enabled automatically.)

Examples

When one or more terms are given, the list is processed sequentially from left to right, thus -ftrap=%all,no%inexact means to set all traps except inexact.

Interactions

The mode can be changed at runtime with ieee_handler(3M).

Warnings

If you compile one routine with -ftrap=t, compile all routines of the program with the same -ftrap=t option; otherwise, you might get unexpected results.

Use the -ftrap=inexact trap with caution. Use of -ftrap=inexact results in the trap being issued whenever a floating-point value cannot be represented exactly. For example, the following statement generates this condition:

x = 1.0 / 3.0;

This option is effective only if used when compiling the main program. Be cautious when using this option. If you wish to enable the IEEE traps, use -ftrap=common.