The floating-point environment is the set of floating-point status flags and control modes supported by the implementation. It is thread-local, each thread inherits the initial state of its floating-point environment from the parent thread. Floating-point operations modify the floating-point status flags to indicate abnormal results or auxiliary information. The state of floating-point control modes affects the outcomes of some floating-point operations.
The floating-point environment access and modification is only meaningful when
#pragma STDC FENV_ACCESS is set to
ON. Otherwise the implementation is free to assume that floating-point control modes are always the default ones and that floating-point status flags are never tested or modified. In practice, few current compilers support the
#pragma explicitly, but most compilers allow meaningful access to the floating-point environment anyway.
Defined in header
|fenv_t||The type representing the entire floating-point environment|
|fexcept_t||The type representing all floating-point status flags collectively|
The floating-point exceptions are not related to the C++ exceptions. When a floating-point operation raises a floating-point exception, the status of the floating-point environment changes, which can be tested with std::fetestexcept, but the execution of a C++ program on most implementations continues uninterrupted.
There are compiler extensions that may be used to generate C++ exceptions automatically whenever a floating-point exception is raised:
- GNU libc function
feenableexcept()enables trapping of the floating-point exceptions, which generates the signal
SIGFPE. If the compiler option
-fnon-call-exceptionswas used, the handler for that signal may throw a user-defined C++ exception.
- Microsoft WinAPI function
_control87()enables trapping of the floating-point exceptions, which generates a hardware exception, which can be converted to C++ exceptions with