std::numeric_limits::traps - cppreference.com (original) (raw)
| static const bool traps; | | (until C++11) | | ---------------------------- | | ------------- | | static constexpr bool traps; | | (since C++11) |
The value of std::numeric_limits<T>::traps is true for all arithmetic types T that have at least one value at the start of the program that, if used as an argument to an arithmetic operation, will generate a trap.
[edit] Standard specializations
| T | value of std::numeric_limits<T>::traps |
|---|---|
| /* non-specialized */ | false |
| bool | false |
| char | usually true |
| signed char | usually true |
| unsigned char | usually true |
| wchar_t | usually true |
| char8_t (since C++20) | usually true |
| char16_t (since C++11) | usually true |
| char32_t (since C++11) | usually true |
| short | usually true |
| unsigned short | usually true |
| int | usually true |
| unsigned int | usually true |
| long | usually true |
| unsigned long | usually true |
| long long (since C++11) | usually true |
| unsigned long long (since C++11) | usually true |
| float | usually false |
| double | usually false |
| long double | usually false |
[edit] Notes
On most platforms integer division by zero always traps, and std::numeric_limits<T>::traps is true for all integer types that support the value 0. The exception is the type bool: even though division by false traps due to integral promotion from bool to int, it is the zero-valued int that traps. Zero is not a value of type bool.
On most platforms, floating-point exceptions may be turned on and off at run time (e.g. feenableexcept() on Linux or _controlfp on Windows), in which case the value of std::numeric_limits<T>::traps for floating-point types reflects the state of floating-point trapping facility at the time of program startup, which is false on most modern systems. An exception would be a DEC Alpha program, where it is true if compiled without -ieee.
[edit] Example
Possible output:
// GCC output: bool: traps = true char: traps = true char16_t: traps = true long: traps = true float: traps = false // Clang output: bool: traps = false char: traps = true char16_t: traps = true long: traps = true float: traps = false
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 497 | C++98 | it was unclear what is returned if trappingis enabled or disabled at runtime | returns the enable statusat the start of the program |