std::numeric_limits<T>::traps

 

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numeric_limits::denorm_min

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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.

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

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.

Example

Run this code

#include <iostream>
#include <limits>
 
int main()
{
    std::cout << std::boolalpha
              << "bool:     traps = " << std::numeric_limits<bool>::traps << '\n'
              << "char:     traps = " << std::numeric_limits<char>::traps << '\n'
              << "char16_t: traps = " << std::numeric_limits<char16_t>::traps << '\n'
              << "long:     traps = " << std::numeric_limits<long>::traps << '\n'
              << "float:    traps = " << std::numeric_limits<float>::traps << '\n';
}

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

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 trapping is enabled or disabled at runtime	returns the enable status at the start of the program

See also

Floating-point environment
tinyness_before [static]	identifies floating-point types that detect tinyness before rounding (public static member constant)
has_denorm_loss [static]	identifies the floating-point types that detect loss of precision as denormalization loss rather than inexact result (public static member constant)