Re: C++ way to convert ASCII digits to Integer?

From:

pjb@informatimago.com (Pascal J. Bourguignon)

Newsgroups:

comp.lang.c++

Date:

Wed, 27 May 2009 10:51:44 +0200

Message-ID:

<7cr5yb53of.fsf@pbourguignon.anevia.com>

"andreas.koestler@googlemail.com" <andreas.koestler@googlemail.com> writes:

From: blargg <blargg.ei3@gishpuppy.com>
andreas.koestler wrote:

On May 27, 9:18?am, "Peter Olcott" <NoS...@SeeScreen.com> wrote:

I remember that there is a clean C++ way to do this [convert
ASCII digits to Integer], but, I forgot what it was.

I don't know what you mean by 'clean C++ way' but one way to do it is:

int ascii_digit_to_int ( const char asciidigit ) {
  if ( asciidigit < '0' ||
       asciidigit > '9' ) {
    throw NotADigitException();
  }
  return (int) asciidigit - 48; // 48 => '0'
}

Or you can use atoi or similar.
Or you use the std::stringstream:
Not if the machine doesn't use ASCII; only a function like yours above
is fully portable. But perhaps the original poster wanted a function
that would convert from the host's native textual representation to an
integer, in which case the above function would not be a good idea, and
atoi or stringstream would.

Blargg, please explain... :)

Actually Blargg's code is wrong. On a machine using EBCDIC '0' = 248, not 48.

#include <iso646.h>

struct ASCII {
  enum ASCII {
     NUL = 0, SOH, STX, ETX, EOT, ENQ, ACK, BELL, BACKSPACE, TAB,
     NEWLINE, VT, PAGE, RETURN, SO, SI, DLE, DC1, DC2, DC3, DC4, NAK,
     SYN, ETB, CAN, EM, SUB, ESCAPE, FS, GS, RS, US, SPACE,
     EXCLAMATION_MARK, QUOTATION_MARK, NUMBER_SIGN, DOLLAR_SIGN,
     PERCENT_SIGN, AMPERSAND, APOSTROPHE, LEFT_PARENTHESIS,
     RIGHT_PARENTHESIS, ASTERISK, PLUS_SIGN, COMMA, HYPHEN_MINUS,
     FULL_STOP, SOLIDUS, DIGIT_ZERO, DIGIT_ONE, DIGIT_TWO,
     DIGIT_THREE, DIGIT_FOUR, DIGIT_FIVE, DIGIT_SIX, DIGIT_SEVEN,
     DIGIT_EIGHT, DIGIT_NINE, COLON, SEMICOLON, LESS_THAN_SIGN,
     EQUALS_SIGN, GREATER_THAN_SIGN, QUESTION_MARK, COMMERCIAL_AT,
     LATIN_CAPITAL_LETTER_A, LATIN_CAPITAL_LETTER_B,
     LATIN_CAPITAL_LETTER_C, LATIN_CAPITAL_LETTER_D,
     LATIN_CAPITAL_LETTER_E, LATIN_CAPITAL_LETTER_F,
     LATIN_CAPITAL_LETTER_G, LATIN_CAPITAL_LETTER_H,
     LATIN_CAPITAL_LETTER_I, LATIN_CAPITAL_LETTER_J,
     LATIN_CAPITAL_LETTER_K, LATIN_CAPITAL_LETTER_L,
     LATIN_CAPITAL_LETTER_M, LATIN_CAPITAL_LETTER_N,
     LATIN_CAPITAL_LETTER_O, LATIN_CAPITAL_LETTER_P,
     LATIN_CAPITAL_LETTER_Q, LATIN_CAPITAL_LETTER_R,
     LATIN_CAPITAL_LETTER_S, LATIN_CAPITAL_LETTER_T,
     LATIN_CAPITAL_LETTER_U, LATIN_CAPITAL_LETTER_V,
     LATIN_CAPITAL_LETTER_W, LATIN_CAPITAL_LETTER_X,
     LATIN_CAPITAL_LETTER_Y, LATIN_CAPITAL_LETTER_Z,
     LEFT_SQUARE_BRACKET, REVERSE_SOLIDUS, RIGHT_SQUARE_BRACKET,
     CIRCUMFLEX_ACCENT, LOW_LINE, GRAVE_ACCENT, LATIN_SMALL_LETTER_A,
     LATIN_SMALL_LETTER_B, LATIN_SMALL_LETTER_C, LATIN_SMALL_LETTER_D,
     LATIN_SMALL_LETTER_E, LATIN_SMALL_LETTER_F, LATIN_SMALL_LETTER_G,
     LATIN_SMALL_LETTER_H, LATIN_SMALL_LETTER_I, LATIN_SMALL_LETTER_J,
     LATIN_SMALL_LETTER_K, LATIN_SMALL_LETTER_L, LATIN_SMALL_LETTER_M,
     LATIN_SMALL_LETTER_N, LATIN_SMALL_LETTER_O, LATIN_SMALL_LETTER_P,
     LATIN_SMALL_LETTER_Q, LATIN_SMALL_LETTER_R, LATIN_SMALL_LETTER_S,
     LATIN_SMALL_LETTER_T, LATIN_SMALL_LETTER_U, LATIN_SMALL_LETTER_V,
     LATIN_SMALL_LETTER_W, LATIN_SMALL_LETTER_X, LATIN_SMALL_LETTER_Y,
     LATIN_SMALL_LETTER_Z, LEFT_CURLY_BRACKET, VERTICAL_LINE,
     RIGHT_CURLY_BRACKET, TILDE, RUBOUT
}}

int ascii_digit_to_int ( const char asciidigit ) {
    if((asciidigit<ASCII.DIGIT_ZERO)or(ASCII.DIGIT_NINE<asciidigit)){
        throw NotADigitException();
    }else{
       return((int)asciidigit - ASCII.DIGIT_ZERO);
    }
}

--
__Pascal Bourguignon__