Thread: How to convert float to string without using sprintf()

EX:
float a = 88.88888;
char *s = "88.88888"

ps: how to write float into binary file and how to read it?

Why do you want to avoid sprintf? It's the preferred solution according to my cursory looks at Google. Anyway's here's the other way:

Code:

ECVT(3)                    Linux Programmer's Manual                   ECVT(3)

NAME
       ecvt, fcvt - convert a floating-point number to a string

SYNOPSIS
       #include <stdlib.h>

       char *ecvt(double number, int ndigits, int *decpt, int *sign);

       char *fcvt(double number, int ndigits, int *decpt, int *sign);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       ecvt(), fcvt(): _SVID_SOURCE || _XOPEN_SOURCE >= 500

DESCRIPTION
       The  ecvt()  function  converts  number  to a null-terminated string of
       ndigits digits (where ndigits is reduced  to  a  system-specific  limit
       determined  by the precision of a double), and returns a pointer to the
       string.  The high-order digit is nonzero, unless number is  zero.   The
       low order digit is rounded.  The string itself does not contain a deci‐
       mal point; however, the position of the decimal point relative  to  the
       start  of  the string is stored in *decpt.  A negative value for *decpt
       means that the decimal point is to the left of the start of the string.
       If  the  sign  of  number is negative, *sign is set to a nonzero value,
       otherwise it is set to 0.  If number is zero, it is unspecified whether
       *decpt is 0 or 1.

       The  fcvt() function is identical to ecvt(), except that ndigits speci‐
       fies the number of digits after the decimal point.

RETURN VALUE
       Both the ecvt() and fcvt() functions  return  a  pointer  to  a  static
       string  containing  the  ASCII  representation  of  number.  The static
       string is overwritten by each call to ecvt() or fcvt().

Clearly these functions are harder to use, which seems to be why sprintf is preferred.

Originally Posted by liyanhong

EX:
float a = 88.88888;
char *s = "88.88888"

Try strtod (C89).

Originally Posted by BillyTKid

Try strtod (C89).

The title of this post is "How to convert float to string without using sprintf()"

The man page for strtod says "convert ASCII string to floating-point number."

It could be that I totally forgot how to read, but that seems like the precise opposite of what the OP asked for.