Floating-point environment
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.
Types
| Defined in header
<cfenv> | |
| fenv_t | The type representing the entire floating-point environment |
| fexcept_t | The type representing all floating-point status flags collectively |
Functions
| (C++11) |
clears the specified floating-point status flags (function) |
| (C++11) |
determines which of the specified floating-point status flags are set (function) |
| (C++11) |
raises the specified floating-point exceptions (function) |
| (C++11)(C++11) |
copies the state of the specified floating-point status flags from or to the floating-point environment (function) |
| (C++11)(C++11) |
gets or sets rounding direction (function) |
| (C++11) |
saves or restores the current floating point environment (function) |
| (C++11) |
saves the environment, clears all status flags and ignores all future errors (function) |
| (C++11) |
restores the floating-point environment and raises the previously raise exceptions (function) |
Macros
| floating-point exceptions (macro constant) | |
| floating-point rounding direction (macro constant) | |
| (C++11) |
default floating-point environment (macro constant) |
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.
See also
| C documentation for Floating-point environment
|