Re: New Line Constant Error!
From: Chakkaradeep (Chakkaradeep_at_discussions.microsoft.com)
Date: 01/26/05
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Date: Wed, 26 Jan 2005 01:03:06 -0800
Hi Joakim and Bruce,
Thanks a lot, i clearly understood this "new line thing" and i really thank
Bruce and Joakim for their Explanation.Good Job Guys..keep it up!
with regards,
C.C.Chakkaradeep
"Bruce Wood" wrote:
> In C# (as in C and C++), the backslash character ("\") has special
> meaning: it is an "escape" that combines with the character after it to
> make a special character that you can't type into your program. Some
> famous uses of it, all the way back to C, are \n for a newline
> (linefeed) control character, and \0 meaning the character with value 0
> (the NUL control character).
>
> So, any time you type a string and put a backslash \ in it, the
> compiler thinks that you want to indicate a special character, and
> tries to combine the backslash with the following character to create
> something else.
>
> However, what if you really want a backslash character in your string?
> What if you want \n to mean not a newline control character, but really
> a backslash followed by an en? Then you have to use a double-backslash,
> \\, which the compiler reads as a special sequence that folds down into
> a single backslash in the string itself.
>
> Take a look at the following code:
>
> string a = "\n";
> string b = "\\n";
>
> The string called "a" contains a _single character_: a newline, or
> linefeed control character, because the sequence backslash-en is
> interpreted by the compiler as a request for this special character.
>
> The string called "b" contains _two characters_: a backslash, which the
> compiler put into the string because it saw the "escaped backslash"
> sequence: two backslashes in a row... followed by an en character.
>
> Now in C and C++ this was all there was to it: everywhere in your
> string that you wanted a single backslash character, you had to type
> two into your program so that the compiler would know what to do. If
> you wanted two, you would have to type four into your program, etc.
> (Note that this is only the _compiler_ doing this, not the runtime. So,
> if you read in a line from a file that has the characters "\n" on it,
> these do _not_ get folded into a newline character, because the
> _compiler_ isn't reading the file... your program is.)
>
> However, because C# runs on the Windows operating system, and Windows
> traditionally uses backslash to separate directory names in file paths,
> Microsoft realized that forcing you to type double-backslashes for
> every backslash you wanted in a hard-coded string in your program was
> going to be... well, a pain in the ass. So, they added a new marker,
> the "@" marker.
>
> When you put an "@" at the beginning of a string, it means, "Compiler:
> there are no special characters in this string. Don't do your normal
> special-character processing on this one. Just put exactly what I type
> into the string." So, the declaration for string "b" above could be
> changed to:
>
> string b = @"\n";
>
> which produces the same thing internally: a two-character string
> containing a backslash and an en.
>
> In answer to your specific question, the compiler gives you an error
> because you said:
>
> int n = str_old.IndexOf('\');
>
> In this case, the backslash indicates a special character sequence, and
> the following character is a single quote. That tells the compiler that
> you really want a single quote mark in the character sequence, and that
> the single quote that directly follows the backslash is _not_ the
> ending delimiter for the character sequence. So, the compiler goes on
> adding characters to the sequence (closed parenthesis, then semicolon)
> until it arrives at the end of the line and realizes that something
> went wrong. In effect, you never ended the character constant because
> you told the compiler that the second single quote was "special" by
> preceding it with a backslash.
>
> As Joakim pointed out, you could fix this by either doubling the
> backslash, a la C:
>
> int n = str_old.IndexOf('\\');
>
> or adding the "@" marker to the start, to tell the compiler not to
> treat the backslash specially:
>
> int n = str_old.IndexOf(@'\');
>
>
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