How to convert string format number (22.123) to float variable format without using any API in C ++

Question

How to convert string format number (22.123) to float variable format without using any API in C ++. This is just to better understand internal coding .. thnx

Answer 1

sort of:

double string_to_double(std::string s)
{
    int p = 0;
    int p_dec = s.length();

    double val = 0;

    for (int i=0; i<s.length(); ++i)
    {
        double digit = (double)(s[i] - '0');
        if (s[i] == '.') { p_dec = p; }
        else { val += digit*powf(10,p--); }
    }

    val /= powf(10, p_dec);
}

Answer 2

The main algorithm that does not accept input in the form 1.2e-4:

(1) Read the integer before the dot. If the number of digits is> 16 (normal precision double), convert that integer to a floating point directly and return.

(2) 16 . ( ) ; 10 . (1) .

2 : + & divide;, . 10 , .

( 16- , 64- int.)

---

sscanf(str, "%lf", ...), std::istringstream boost::lexical_cast<double>.

Answer 3

, 10 .

Answer 4

, , , , , . : ftp://ftp.ccs.neu.edu/pub/people/will/howtoread.ps

Answer 5

, Plauger Standard C Library strtod. http://www.amazon.co.uk/Standard-C-Library-P-J-Plauger/dp/0131315099

-: http://www.google.co.uk/search?hl=en&client=firefox-a&hs=IvI&rls=org.mozilla%3Aen-GB%3Aofficial&q=strtod+source+code