_gcvt - Convert Floating-Point to String

Syntax

#include <stdlib.h>
char *_gcvt(double value, int ndec, char *buffer);

gcvt converts a floating-point value to a character string pointed to by buffer. The buffer should be large enough to hold the converted value and a null character (\0) that _gcvt automatically adds to the end of the string. There is no provision for overflow.
_gcvt tries to produce ndec significant digits in FORTRAN F format. Failing that, it produces ndec significant digits in FORTRAN E format. Trailing zeros might be suppressed in the conversion if they are significant.
A FORTRAN F number has the following format: ┌──────────────────────────────────────────────────────────────────────────────┐
│ │
│ ┌───────┐ ┌───────────┐ │
│ │ │ │
│ >>──┬───┬────digit─┴──.────┬───────┬─┴──>< │
│ ├─+─┤ └─digit─┘ │
│ └─┴─┘ │
│ │
└──────────────────────────────────────────────────────────────────────────────┘

A FORTRAN E number has the following format: ┌──────────────────────────────────────────────────────────────────────────────┐
│ │
│ ┌───────┐ ┌───────────┐ │
│ │ │ │
│ >>──┬───┬──digit──.────digit─┴──E──┬───┬──digit────┬───────┬─┴──>< │
│ ├─+─┤ ├─+─┤ └─digit─┘ │
│ └─┴─┘ └─┴─┘ │
│ │
└──────────────────────────────────────────────────────────────────────────────┘

_gcvt also converts NaN and infinity values to the strings NAN and INFINITY, respectively. For more information on NaN and infinity values, see Infinity and NaN Support.

Warning: For each thread, _ecvt, _fcvt and _gcvt use a single, dynamically allocated buffer for the conversion. Any subsequent call that the same thread makes to these functions destroys the result of the previous call.

gcvt returns a pointer to the string of digits. If it cannot allocate memory to perform the conversion, _gcvt returns an empty string and sets errno to ENOMEM.

This example converts the value -3.1415e3 to a character string and places it in the character array buffer1. It then converts the macro value _INF to a character string and places it in buffer2.

#include <stdio.h>
#include <stdlib.h>
#include <float.h>                  /* for the definition of _INF             */

int main(void)
{
   char buffer1[10],buffer2[10];

   _gcvt(-3.1415e3, 7, buffer1);
   printf("The first result is %s \n", buffer1);
   _gcvt(_INF, 5, buffer2);
   printf("The second result is %s \n", buffer2);
   return 0;

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

      The first result is -3141.5
      The second result is INFINITY
   ****************************************************************************/
}

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