char [0-9] to int [0-9]

[pete]

Martin Jørgensen said:

I count five. Is this a case of one, two, three, er, many?

4 arithmetic operations and one relational operation.
I consider the relational operation to be more like a decission,
like an if statement or a conditional operator,
than like a calculation.

 

[CBFalconer]

Peter Jansson said:

Gladly. Instead of writing:

n = char_to_int(ch);

write:

n = ch - '0';

And indeed that's what I do in my own code. It may be objected
that recent versions of char_to_int have range checks, and return
-1 if an out-of-range value is passed. But this means that you
have to do something like: ... snip ...

Provided n and ch are unsigned, then the test is simple:

if ((n = ch - '0') > 9) barfloudly();

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[Dale Henderson]

RH> Neither would I. The consensus appears to be that the whole
RH> function is a complete waste of time.

I never intended it as a real solution.

RH> But Dale's code is still neat.

Take some credit, I only debuged your code.

 

[Richard Bos]

atoi
a2i

What does a-twee-i have to do with atoi? Why is the first macro called
CHAR-zwei-DIGIT? Why is the second called DIGIT-deux-CHAR?

Richard

 

[pete]

What does a-twee-i have to do with atoi? Why is the first macro called
CHAR-zwei-DIGIT? Why is the second called DIGIT-deux-CHAR?

I don't know.

I don't take languages that I don't know,
into consideration, when I write.
I'm American,
so I only know some of the American dialects of English.

 

[Richard Bos]

I don't know.

I don't take languages that I don't know,
into consideration, when I write.
I'm American,
so I only know some of the American dialects of English.

Ok, let's try again, for the nil-lingual:

What happened to CHAR1DIGIT? Was it an inferior version? Will we get a
DIGIT3CHAR at some point?

Richard

 

[pete]

Ok, let's try again, for the nil-lingual:

What happened to CHAR1DIGIT?

If there was a way that a char could win a digit,
and I wanted to determine if that had happened,
I might write CHAR1DIGIT instead of CHARWONDIGIT.

 

[pete]

If there was a way that a char could win a digit,
and I wanted to determine if that had happened,
I might write CHAR1DIGIT instead of CHARWONDIGIT.

I think now I'm getting a little silly.

My point is that I've seen Martin Ambuhl's
naming convention in code before, and I've used it,
and when I was asked what my list_x2x function did,
I was asked about what was converted "to" what.

 

[Robert Latest]

["Followup-To:" header set to comp.lang.c.]

What if there was a system where the digits '0' through '9' is not
continuous? Would the standard translate them to a continuous
representation?

This is what the Standard has to say about the topic:

In both the source and execution basic character sets,
the value of each character after 0 in the above list of
decimal digits shall be one greater than the value of
the previous.

What I don't understand is why the consecutivity of 0 thru 9 is
required from the *source* character set as well. In case source
and execution set differ, won't the compiler have to translate
all character constants and string literals anyway?

robert

 

[tedu]

Why is the first macro called CHAR-zwei-DIGIT?

maybe he thought it sounded better than BUCHSTABEZWEISTELLE.

if one doesn't know english, who would CHARTODIGIT be any more clear?

 

[Duane Hebert]

maybe he thought it sounded better than BUCHSTABEZWEISTELLE.

if one doesn't know english, who would CHARTODIGIT be any more clear?

If you want to chart an odigit. Maybe char_to_digit or charToDigit or
something...

 

[Victor Bazarov]

If you want to chart an odigit. Maybe char_to_digit or charToDigit or
something...

For those who don't know English, does 'char' or 'digit' mean the same
thing as for those who do know it? Then would it be possible that when
they read the name, instead of thinking 'zwei', they do think 'two',
simply because they are in the "English" mode? Just a thought...

 

[Alex Buell]

For those who don't know English, does 'char' or 'digit' mean the same
thing as for those who do know it? Then would it be possible that
when they read the name, instead of thinking 'zwei', they do think
'two', simply because they are in the "English" mode? Just a
thought...

In English, my fingers are also 'digits'.

 

[Walter Bright]

In C++ it's no big deal to define a non-macro conversion that yields a
compile time constant:

template< char digit >
struct IntFromDigit { enum{ value = digit - '\0' }; };

...
int array[IntFromDigit<'7'>::value];

If that conversion were ever required, it would be in template code, so
a template solution is very fitting.

Just use:

(digit - '0')

and be done with it.

 

[Vladimir Oka]

Victor Bazarov opined:

For those who don't know English, does 'char' or 'digit' mean the
same thing as for those who do know it?

For those who don't know English, both mean absolutely nothing at all
(unless they speak Latin, or their native language is of Romance
descent, in which case they may get the "digit").

Then would it be possible that when they read the name, instead of
thinking 'zwei', they do think 'two', simply because they are in the
"English" mode? Just a thought...

Using "2" for "to" became commonplace in software circles, so I doubt
it's misleading. OTH, I still mentally read out all the numbers (apart
from char2digit variety) in my native language, even in English mode
(and I'm in English mode for at least 75% of my waking hours). YMMV.

 

[Alf P. Steinbach]

* Walter Bright:

In C++ it's no big deal to define a non-macro conversion that yields a
compile time constant:

template< char digit >
struct IntFromDigit { enum{ value = digit - '\0' }; };

...
int array[IntFromDigit<'7'>::value];

If that conversion were ever required, it would be in template code,
so a template solution is very fitting.

Just use:

(digit - '0')

and be done with it.

What I wrote was, just use the number 7. ;-)

 

[Vladimir Oka]

Vladimir Oka opined:

Victor Bazarov opined:


For those who don't know English, both mean absolutely nothing at all
(unless they speak Latin, or their native language is of Romance
descent, in which case they may get the "digit").

Not to mention that, out of context, "char" can be construed as a
variant of "charcoal", especially if, in a different life, one was
involved in coal combustion. ;-)

 

[Victor Bazarov]

Vladimir Oka opined:


Not to mention that, out of context, "char" can be construed as a
variant of "charcoal", especially if, in a different life, one was
involved in coal combustion. ;-)

Yeah, yeah... And "char2digit" means "Zwei parts ashes, ein part finger"
(analogous to H2O), right?

 

[crichmon]

Is there an elegant way to do something like

// given a char {0,1,2,3,4,5,6,7,8,9} returns it as a short
short char2digit(char c)
{
short d = c-48;
return d;
}

?

Thanks.

int char_to_digit(const char & chardigit)
{
static const int zeroindex = static_cast<int>('0');

int digit = (static_cast<int>(chardigit) - zeroindex);

if ((digit > 9) || (digit < 0)) return -1; // or throw an exception

return digit;
};

 

[crichmon]

oops, rather

short char_to_digit(const char & chardigit)
{
static const short zeroindex = static_cast<short>('0');

short digit = (static_cast<short>(chardigit) - zeroindex);

if ((digit > 9) || (digit < 0)) return -1; // or throw an exception
else return digit;
};