Difference between revisions of "cpp/numeric/math/nan"

Revision as of 05:26, 15 September 2021

Converts the implementation-defined character string arg into the corresponding quiet NaN value, as if by calling the appropriate parsing function strtoX, as follows:

• The call std::nan("n-char-sequence"), where n-char-sequence is a sequence of digits, Latin letters, and underscores, is equivalent to the call /*strtoX*/("NAN(n-char-sequence)", (char**)nullptr);.
• The call std::nan("") is equivalent to the call /*strtoX*/("NAN()", (char**)nullptr);.
• The call std::nan("string"), where string is neither an n-char-sequence nor an empty string, is equivalent to the call /*strtoX*/("NAN", (char**)nullptr);.

Parameters

Return value

The quiet NaN value that corresponds to the identifying string arg or zero if the implementation does not support quiet NaNs.

If the implementation supports IEEE floating-point arithmetic (IEC 60559), it also supports quiet NaNs.

Error handling

This function is not subject to any of the error conditions specified in math_errhandling.

Example

#include <iostream>
#include <cmath>
#include <cstdint>
#include <cstring>
 
int main()
{
    double f1 = std::nan("1");
    std::uint64_t f1n; std::memcpy(&f1n, &f1, sizeof f1);
    std::cout << "nan(\"1\") = " << f1 << " (" << std::hex << f1n << ")\n";
 
    double f2 = std::nan("2");
    std::uint64_t f2n; std::memcpy(&f2n, &f2, sizeof f2);
    std::cout << "nan(\"2\") = " << f2 << " (" << std::hex << f2n << ")\n";
}

nan("1") = nan (7ff0000000000001)
nan("2") = nan (7ff0000000000002)

See also