atof with base information

[skiflyer]

I'm trying to convert strings to base 10 integers... but I'm not starting in base 10, so what I'm looking for would basically be an atof function where I can also supply a base... anyone know if this is possible with built in functions, or am I writing this?

 

[uolj]

It depends on what base the string is in. If it is in binary, use bitset. If it is in hexadecimal or octal, use a stringstream. Here's some examples:

#include <iostream>
#include <string>
#include <bitset>
#include <sstream>

int main()
{
    int value = 0;

    std::string binary = "11110001001000000";
    std::bitset<sizeof(int)*8> bs(binary);
    value = bs.to_ulong();
    std::cout << binary << " converts to " << value << '\n';

    std::string octal = "0361100"; // Leading 0 not necessary.
    std::istringstream iso(octal);
    iso >> std::oct >> value;
    std::cout << octal << " converts to " << value << '\n';

    std::string hexadecimal = "0x1E240"; // Leading 0x not necessary.
    std::istringstream ish(hexadecimal);
    ish >> std::hex >> value;
    std::cout << hexadecimal << " converts to " << value << '\n';
}

 

[skiflyer]

it's just an arbitrary base between 16-35. I've already written a simple function to convert it, but I figured if there's already a nice built in method to do so I should probably be using that.

 

[uolj]

Ok. I Personally don't know of any existing functions that would do that.

Good luck with your own. You could always post it here for tips and comments.

 

[cpjust]

I've already written a simple function to convert it

I did that a few years ago too (just for fun). Once you look at the source code for the atoi() function, it's easy to specify just about any base. ;-)

 

[skiflyer]

Lifted from a codeproject article (I need to tweak it a bit yet to updated the deprecated functions)

int StrToNum(const TCHAR *udata, int udatalen, int base)
{
	long index;
	const TCHAR numdigits[] = 
		TEXT("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ");
	long digitValue = 0;
	long RetVal = 0;
	TCHAR digits[sizeof(numdigits)+1];
	TCHAR *dataVal;
	TCHAR data[512];

	_tcscpy(data, udata);
	_tcsupr(data);

	ZeroMemory(digits, sizeof(digits));

	_tcsncpy(digits, numdigits, base);

	for(index = 0; index < udatalen; index++)
	{
		dataVal = _tcschr(digits, data[index]);
		if (dataVal != 0)
		{
			digitValue = long(dataVal - digits);
			RetVal = RetVal * base + digitValue;
		}
	}
	return RetVal;
}

 

[ArkM]

Remember strtol from <cstdlib>:

long strtol( const char *nptr, char **endptr, int base );

The base arg is between 2 and 36 (or a special case 0, see strtol description).

 

[cpjust]

Other than doing it out of bordom, is there any reason why anyone would ever need to use a base other than 2, 8, 10 or 16? Base 36 seems a little ridiculous...

 

[skiflyer]

I use a rolling base on my registration keys just to shuffle them up a bit and to guarantee me two digits for each ASCII character. (16-35 base will give you said guarantee)... plus that way I can tweak it a bit to never have an O(letter oh)... by stopping at base 35 and swapping the O's for Z's in my strings so they won't be confused with the zeros.

 

[cpjust]

I've never had the need to use a non-standard base myself, but I guess it makes sense for something like that.