Re: Lexical conversion.

[John Carter <john.carter@tait.co.nz>]

On Tue, 15 Oct 2002, Claudio Bley wrote:
> >>>>> "John" == John Carter <john.carter@tait.co.nz> writes:
> 
>     John> What is the fastest way under gcc-3.* to convert from an int
>     John> to a string?  ie. Equivalent to this yucky bit of code...
> 
> We are talking about C++, right? I don't know how fast it is (or what
> your constrains are), but I would use something like that:
> 
> #include <sstream>
> 
> string convert (const int number) {
>      ostringstream ostr;
>      ostr << number;
>      return ostr.str ();
> }

Sigh! I decided (especially as most the cases I worry about are in 0-9) to 
implement it like so.. (I unit tested it so I'm reasonable confident it 
works and its about 3 times faster in the general case than using printf)

string convert(const int value) {
  int abs_value;

  if (value >= 0) {
    // Optimise for single digit case...
    if (value <= 9) {
      return string( 1, '0'+value);
    }

    abs_value = value;
  } else {
    abs_value = -value;
  }

  char buf[100];
  char * start = buf+100;
  char * end = start;

  do {
    *(--start) = '0' + abs_value % 10;
    abs_value /= 10;
  } while (abs_value);
  
  if( value < 0) {
    *(--start) = '-';
  }

  return string(start, end-start);
}


-- 


John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

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