### 7.4 Conversion Functions

Function: double mpf_get_d (const mpf_t op)

  Convert op to a `double`, truncating if necessary (i.e. rounding towards zero).

  If the exponent in op is too big or too small to fit a `double` then the result is system dependent. For too big an infinity is returned when available. For too small 0.0 is normally returned. Hardware overflow, underflow and denorm traps may or may not occur.

Function: double mpf_get_d_2exp (signed long int *exp, const mpf_t op)

  Convert op to a `double`, truncating if necessary (i.e. rounding towards zero), and with an exponent returned separately.

  The return value is in the range 0.5<=abs(d)<1 and the exponent is stored to `*exp`. d * 2^exp is the (truncated) op value. If op is zero, the return is 0.0 and 0 is stored to `*exp`.

  This is similar to the standard C `frexp` function (see Normalization Functions in The GNU C Library Reference Manual).

Function: long mpf_get_si (const mpf_t op)
Function: unsigned long mpf_get_ui (const mpf_t op)

  Convert op to a `long` or `unsigned long`, truncating any fraction part. If op is too big for the return type, the result is undefined.

  See also `mpf_fits_slong_p` and `mpf_fits_ulong_p` (see Miscellaneous Float Functions).

Function: char * mpf_get_str (char *str, mp_exp_t *expptr, int base, size_t n_digits, const mpf_t op)

  Convert op to a string of digits in base base. The base argument may vary from 2 to 62 or from -2 to -36. Up to n_digits digits will be generated. Trailing zeros are not returned. No more digits than can be accurately represented by op are ever generated. If n_digits is 0 then that accurate maximum number of digits are generated.

  For base in the range 2..36, digits and lower-case letters are used; for -2..-36, digits and upper-case letters are used; for 37..62, digits, upper-case letters, and lower-case letters (in that significance order) are used.

  If str is `NULL`, the result string is allocated using the current allocation function (see Custom Allocation). The block will be `strlen(str)+1` bytes, that being exactly enough for the string and null-terminator.

  If str is not `NULL`, it should point to a block of n_digits + 2 bytes, that being enough for the mantissa, a possible minus sign, and a null-terminator. When n_digits is 0 to get all significant digits, an application won’t be able to know the space required, and str should be `NULL` in that case.

  The generated string is a fraction, with an implicit radix point immediately to the left of the first digit. The applicable exponent is written through the expptr pointer. For example, the number 3.1416 would be returned as string `"31416"` and exponent 1.

  When op is zero, an empty string is produced and the exponent returned is 0.

  A pointer to the result string is returned, being either the allocated block or the given str.