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digitalmars.D.learn - Converting char to int

reply "Caeadas" <mitch.m13 hotmail.com> writes:
I hope you'll forgive my asking an overly easy question: I've
been searching for an answer and having trouble finding one, and
am getting frustrated.

My issue is this: I'm trying to convert character types to
integers using to!int from std.conv, and I'm getting, for
example, '0'->48, '1'->49, etc. It seems like there should be a
simple way around this, but it's eluding me.
Dec 31 2013
next sibling parent "thedeemon" <dlang thedeemon.com> writes:
On Wednesday, 1 January 2014 at 06:21:05 UTC, Caeadas wrote:

 My issue is this: I'm trying to convert character types to
 integers using to!int from std.conv, and I'm getting, for
 example, '0'->48, '1'->49, etc. It seems like there should be a
 simple way around this, but it's eluding me.


Well, in ASCII (as well as UTF-8 and many others) the character 
'0' is represented by number 48, character '1' is 49 etc., so if 
you want to convert '5' to 5 you just need to subtract '0's 
number from it, e.g.
char c = ...;
int x = c - '0';
Dec 31 2013
prev sibling parent reply "Meta" <jared771 gmail.com> writes:
On Wednesday, 1 January 2014 at 06:21:05 UTC, Caeadas wrote:

 I hope you'll forgive my asking an overly easy question: I've
 been searching for an answer and having trouble finding one, and
 am getting frustrated.

 My issue is this: I'm trying to convert character types to
 integers using to!int from std.conv, and I'm getting, for
 example, '0'->48, '1'->49, etc. It seems like there should be a
 simple way around this, but it's eluding me.


Your code is working correctly. D's chars, for all values up to 
255, are the same as the ASCII character set. If you look in the 
ASCII table here: http://www.asciitable.com/ you will see that 
'0' corresponds to 48, and '1' corresponds to 49. The easiest 
solution that will fix your code is change to!int('0') and 
to!int('1') to to!int("0") and to!int("1"). It seems that for 
characters the to! function just returns its ASCII value, but it 
will definitely do what you want for strings. Strangely enough, 
it doesn't seem like there's a function to do convert a character 
to its numeric value in Phobos, but it's simple to implement.

int charToInt(char c)
{
     return (c >= 48 && c <= 57) ? cast(int)(c - 48) : -1;
}

void main()
{
     assert(charToInt('0') == 0);
     assert(charToInt('1') == 1);
     assert(charToInt('9') == 9);
     assert(charToInt('/') == -1);
     assert(charToInt(':') == -1);
}
Dec 31 2013
next sibling parent reply "Caeadas" <mitch.m13 hotmail.com> writes:
Thanks much for the help, both of you :). I thought there might
be a very simple way to do this, since it's so intuitive to
change '4' to 4. I've basically just been subtracting 48 from
everything, but I suppose aesthetically it's a bit nicer to
convert from string instead.
Jan 01 2014
parent "monarch_dodra" <monarchdodra gmail.com> writes:
On Wednesday, 1 January 2014 at 20:01:56 UTC, Caeadas wrote:

 Thanks much for the help, both of you :). I thought there might
 be a very simple way to do this, since it's so intuitive to
 change '4' to 4.


There have been talks about it, but it hasn't been implemented 
yet. The idea was to provide the function for ascii *once* we've 
implemented it in unicode.


 I've basically just been subtracting 48 from
 everything, but I suppose aesthetically it's a bit nicer to
 convert from string instead.


Don't substract 48. That's just a number! Substract '0' :)

int charToInt(char c)
{
     c -= '0';
     return c <= 9 ? c : -1;
}
Jan 02 2014
prev sibling parent reply Marco Leise <Marco.Leise gmx.de> writes:
Am Wed, 01 Jan 2014 07:27:54 +0000
schrieb "Meta" <jared771 gmail.com>:


 Your code is working correctly. D's chars, for all values up to 
 255, are the same as the ASCII character set.


UTF-8 reuses the ASCII mapping which is only defined from 0 to
127. Everything above is not ASCII and 255 is in fact not even
defined for UTF-8, which is why it was chosen as the
initializer for char in D.

-- 
Marco
Jan 01 2014
parent "Meta" <jared771 gmail.com> writes:
On Wednesday, 1 January 2014 at 20:08:24 UTC, Marco Leise wrote:

 Am Wed, 01 Jan 2014 07:27:54 +0000
 schrieb "Meta" <jared771 gmail.com>:


 Your code is working correctly. D's chars, for all values up 
 to 255, are the same as the ASCII character set.


 UTF-8 reuses the ASCII mapping which is only defined from 0 to
 127. Everything above is not ASCII and 255 is in fact not even
 defined for UTF-8, which is why it was chosen as the
 initializer for char in D.


Yes, I didn't want to cause confusion talking about ASCII vs. 
Unicode.
Jan 01 2014