The string conversion functions that support infinity and NaN representations include the functions: atof, _atold, _ecvt, _fcvt, _gcvt, strtod, strtold, and wcstod.

The atof, _atold, strtod, strtold, and wcstod functions accept the strings INFINITY, INF, and NAN (in uppercase, lowercase, or mixed case) as input, and convert these strings to the corresponding macro value defined in <float.h>. The _ecvt, _fcvt, and _gcvt functions convert infinity and NaN values to the strings INFINITY and NAN, respectively.

Note: If a signaling NaN string is passed to a string conversion function, a quiet NaN value is returned, and no signal is raised.

Example: The following example uses atof to convert the strings "naN" and "inf" to the corresponding macro value.

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

int main(void)
{
   char *nanstr;
   char *infstr;

   nanstr = "naN";
   printf( "Result of atof = %.10e\n", atof(nanstr) );

   infstr = "inf";
   printf( "Result of atof = %.10E\n", atof(infstr) );

   return 0;

   /* The expected output is:

      Result of atof = nan
      Result of atof = INFINITY  */

}

For more information on the individual string conversion functions, refer to the entries for them in Library Functions.

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