The function is defined in <cmath> header file.
nan() prototype
double nan (const char* arg);
Similarly, nanf and nanl return NaN values of type float and long double, respectively.
nan() Parameters
An implementation-specific C-string. If the string is empty, the nan() function returns a generic NaN value.
nan() Return value
The na() function returns quiet NaN value.
Example: nan() function
#include <iostream>
#include <cmath>
#include <cstring>
using namespace std;
int main()
{
double src = nan("1");
uint64_t dest;
// copies variable src to dest
// use <cstring> for memcpy()
memcpy(&dest, &src, sizeof src);
cout << "nan(\"1\") = " << src << " (" << hex << dest << ")\n";
return 0;
}
When you run the program, the output will be:
nan("1") = nan (7ff8000000000001)