# std::numeric_limits<T>::traps

From cppreference.com
< cpp‎ | types‎ | numeric limits

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)

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/types/numeric_limits/traps&oldid=148550"