std::nan, std::nanf, std::nanl
From cppreference.com
| Defined in header <cmath>
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||
float nanf( const char* arg );
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(1) | (since C++11) |
double nan ( const char* arg );
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(2) | (since C++11) |
long double nanl( const char* arg );
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(3) | (since C++11) |
Converts the character string arg into the corresponding quiet NaN value, as if by calling std::strtof, std::strtod, or std::strtold, respectively.
1) The call
std::nanf("n-char-sequence"), where n-char-sequence is a sequence of digits, ASCII letters, and underscores, is equivalent to the call std::strtof("NAN(n-char-sequence)", (char**)nullptr);. The call
std::nanf("") is equivalent to the call std::strtof("NAN()", (char**)nullptr);. The call
std::nanf("string"), where string is neither an n-char-sequence nor an empty string, is equivalent to the call std::strtof("NAN", (char**)nullptr);.2) Same as (1), but calls std::strtod instead of std::strtof.
3) Same as (1), but calls std::strtold instead of std::strtof.
Parameters
| arg | - | narrow character string identifying the contents of a NaN |
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
Run this code
#include <cmath>
#include <cstdint>
#include <cstring>
#include <iostream>
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";
}
Possible output:
nan("1") = nan (7ff0000000000001)
nan("2") = nan (7ff0000000000002)