Floating-point environment (since C++11)
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 supported and 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, such as HP aCC, Oracle Studio, or IBM XL, support the #pragma explicitly, but most compilers allow meaningful access to the floating-point environment anyway.
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[edit] Types
<cfenv> (typedef) [edit]
[edit] Functions
(function) [edit]
(function) [edit]
(function) [edit]
[edit] Macros
[edit] Notes
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 signalSIGFPE. If the compiler option-fnon-call-exceptionswas used, the handler for that signal may throw a user-defined C++ exception. - MSVC function
_control87()enables trapping of the floating-point exceptions, which generates a hardware exception, which can be converted to C++ exceptions with_set_se_translator.