_atold - Convert Character String to Long Double

Syntax

#include <stdlib.h>    /* also defined in <math.h> */
long double _atold(const char *nptr);

atold converts a character string pointed to by nptr to a long double value. The function continues until it reads a character it does not recognize as part of a number. This character can be the ending null character. Except for its behavior on error, _atold is equivalent to:
```
strtold(nptr, (char **)NULL)
```
The string pointed to by nptr must have the following format: ┌──────────────────────────────────────────────────────────────────────────────┐
│ │
│ >>──┬────────────┬──┬────────────────────────────────────────┬──> │
│ └─whitespace─┘ └─┬─────┬──┬─digits──┬───┬──┬────────┬─┬─┘ │
│ ├─ + ─┤ │ └─.─┘ └─digits─┘ │ │
│ └─ ┴ ─┘ └─.──digits─────────────────┘ │
│ │
│ >──┬──────────────────────────┬──>< │
│ └─┬─ e ─┬──┬─────┬──digits─┘ │
│ └─ E ─┘ ├─ + ─┤ │
│ └─ ┴ ─┘ │
│ │
└──────────────────────────────────────────────────────────────────────────────┘

digits is one or more decimal digits. If no digits appear before the decimal point, at least one digit must follow the decimal point. The decimal point character (radix character) is determined by the LC_NUMERIC category of the current locale. You can place an exponent expressed as a decimal integer after the digits. The exponent can be signed.
The value of nptr can also be one of the strings infinity, inf, or nan. These strings are case-insensitive, and can be preceded by a unary minus (-). They are converted to infinity and NaN values. For more information on NaN and infinity values, see Infinity and NaN Support.
_atold ignores any white-space characters, as defined by the isspace function.

atold returns the converted long double value. In the case of an underflow, it returns 0. In the case of a positive overflow, _atold returns positive _LHUGE_VAL. It returns negative _LHUGE_VAL for a negative overflow.

This example uses _atold to convert two strings, " -001234.5678e10end of string" and "NaNQ", to their corresponding long double values.

#include <stdlib.h>
#include <stdio.h>

int main(void)
{
   char *string;

   string = "  -001234.5678e10end of string";
   printf("_atold = %.10Le\n", _atold(string));
   string = "NaNQ";
   printf("_atold = %.10Le\n", _atold(string));
   return 0;

   /****************************************************************************
      The output should be:

      _atold = -1.2345678000e+13
      _atold = nan
   ****************************************************************************/

}

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