GCC libquadmath: quadmath_snprintf

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### 3.2 `quadmath_snprintf` — Convert to string

The function `quadmath_snprintf` converts a `__float128` floating-point number into a string. It is a specialized alternative to `snprintf`, where the format string is restricted to a single conversion specifier with `Q` modifier and conversion specifier `e`, `E`, `f`, `F`, `g`, `G`, `a` or `A`, with no extra characters before or after the conversion specifier. The `%m$` or `*m$` style must not be used in the format.

Syntax

  `int quadmath_snprintf (char *s, size_t size, const char *format, ...)`

Arguments:

  s | output string
  size | byte size of the string, including tailing NUL
  format | conversion specifier string

Note

  On some targets when supported by the C library hooks are installed for `printf` family of functions, so that `printf ("%Qe", 1.2Q);` etc. works too.

Example

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

      int main ()
      {
        __float128 r;
        int prec = 20;
        int width = 46;
        char buf[128];

        r = 2.0q;
        r = sqrtq (r);
        int n = quadmath_snprintf (buf, sizeof buf, "%+-#*.20Qe", width, r);
        if ((size_t) n < sizeof buf)
          printf ("%s\n", buf);
          /* Prints: +1.41421356237309504880e+00 */
        quadmath_snprintf (buf, sizeof buf, "%Qa", r);
        if ((size_t) n < sizeof buf)
          printf ("%s\n", buf);
          /* Prints: 0x1.6a09e667f3bcc908b2fb1366ea96p+0 */
        n = quadmath_snprintf (NULL, 0, "%+-#46.*Qe", prec, r);
        if (n > -1)
          {
            char *str = malloc (n + 1);
            if (str)
              {
                quadmath_snprintf (str, n + 1, "%+-#46.*Qe", prec, r);
                printf ("%s\n", str);
                /* Prints: +1.41421356237309504880e+00 */
              }
            free (str);
          }
        return 0;
      }