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Sign ' is the same as \' ?

P: n/a
Hello everyone,
I am surprised to see that the value of sign ' is the same as \'. So,
there is no need to add sign \ before sign '? In my past knowledge of
sign ', we always need to add sign \ before sign '. Any comments?

Here is my simple program to test.

Expand|Select|Wrap|Line Numbers
  1. #include <string.h>
  2.  
  3. int main (int argc, char** argv)
  4. {
  5. char* p1 = "Hello \'World\'";
  6. char* p2 = "Hello 'World'";
  7. int result = 0;
  8.  
  9. result = strcmp(p1, p2);
  10.  
  11. return 0;
  12. }
  13.  

thanks in advance,
George
Nov 23 '07 #1
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10 Replies


P: n/a
In article <e8**********************************@a39g2000pre. googlegroups.com>,
George2 <ge*************@yahoo.comwrote:
>I am surprised to see that the value of sign ' is the same as \'. So,
there is no need to add sign \ before sign '?
There's no need to put a backslash before a single quote in a string,
but in a character constant you need it:

char *s = "'";
char c = '\'';

Conversely you need a backslash before a double quote in a string, but
not in a character constant:

char *s = "\"";
char c = '"';

You are allowed to use the backslashed forms even when not necessary.

-- Richard
--
"Consideration shall be given to the need for as many as 32 characters
in some alphabets" - X3.4, 1963.
Nov 23 '07 #2

P: n/a
George2 wrote:
Hello everyone,
I am surprised to see that the value of sign ' is the same as \'. So,
there is no need to add sign \ before sign '? In my past knowledge of
sign ', we always need to add sign \ before sign '. Any comments?
This snippet

char ch = 'a';
printf ("It's Jon%cs\n", ch);

.... prints "It's Jonas". Your mission, should you choose to
accept it, is to change the first line to make the output be
"It's Jon's".

--
Eric Sosman
es*****@ieee-dot-org.invalid
Nov 23 '07 #3

P: n/a
Eric Sosman wrote:
George2 wrote:
>Hello everyone,
I am surprised to see that the value of sign ' is the same as \'. So,
there is no need to add sign \ before sign '? In my past knowledge of
sign ', we always need to add sign \ before sign '. Any comments?

This snippet

char ch = 'a';
printf ("It's Jon%cs\n", ch);

... prints "It's Jonas". Your mission, should you choose to
accept it, is to change the first line to make the output be
"It's Jon's".
How do you propose to make your posting self-destruct?
Nov 23 '07 #4

P: n/a
Mark Bluemel wrote:
Eric Sosman wrote:
>George2 wrote:
>>Hello everyone,
I am surprised to see that the value of sign ' is the same as \'. So,
there is no need to add sign \ before sign '? In my past knowledge of
sign ', we always need to add sign \ before sign '. Any comments?

This snippet

char ch = 'a';
printf ("It's Jon%cs\n", ch);

... prints "It's Jonas". Your mission, should you choose to
accept it, is to change the first line to make the output be
"It's Jon's".

How do you propose to make your posting self-destruct?
Unnecessary; I'll just deny all knowledge.

--
Eric Sosman
es*****@ieee-dot-org.invalid
Nov 23 '07 #5

P: n/a

"George2" <ge*************@yahoo.comwrote in message
news:e8**********************************@a39g2000 pre.googlegroups.com...
Hello everyone,
I am surprised to see that the value of sign ' is the same as \'. So,
there is no need to add sign \ before sign '? In my past knowledge of
sign ', we always need to add sign \ before sign '. Any comments?

Here is my simple program to test.

Expand|Select|Wrap|Line Numbers
  1. #include <string.h>
  2. int main (int argc, char** argv)
  3. {
  4. char* p1 = "Hello \'World\'";
  5. char* p2 = "Hello 'World'";
  6. int result = 0;
  7. result = strcmp(p1, p2);
  8. return 0;
  9. }
  10.  
Context, context, context.

char c = '\''; /* apostrophe in character literal */
char *s = "'"; /* apostrophe in string literal */

char c = '"'; /* quote in character literal */
char *s = "\""; /* quote in string literal */

char c = '''; /* invalid */
char *s = """; /* invalid */

-Mike
Nov 23 '07 #6

P: n/a
Eric Sosman wrote:
George2 wrote:
>Hello everyone,
I am surprised to see that the value of sign ' is the same as \'. So,
there is no need to add sign \ before sign '? In my past knowledge of
sign ', we always need to add sign \ before sign '. Any comments?

This snippet

char ch = 'a';
printf ("It's Jon%cs\n", ch);

... prints "It's Jonas". Your mission, should you choose to
accept it, is to change the first line to make the output be
"It's Jon's".
char ch = '\'';

--
Joe Wright
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---
Nov 23 '07 #7

P: n/a
"Mike Wahler" <mk******@mkwahler.neta écrit dans le message de news:
13*************@corp.supernews.com...
>
"George2" <ge*************@yahoo.comwrote in message
news:e8**********************************@a39g2000 pre.googlegroups.com...
>Hello everyone,
I am surprised to see that the value of sign ' is the same as \'. So,
there is no need to add sign \ before sign '? In my past knowledge of
sign ', we always need to add sign \ before sign '. Any comments?

Here is my simple program to test.

Expand|Select|Wrap|Line Numbers
  1. #include <string.h>
  2. int main (int argc, char** argv)
  3. {
  4. char* p1 = "Hello \'World\'";
  5. char* p2 = "Hello 'World'";
  6. int result = 0;
  7. result = strcmp(p1, p2);
  8. return 0;
  9. }

Context, context, context.

char c = '\''; /* apostrophe in character literal */
char *s = "'"; /* apostrophe in string literal */

char c = '"'; /* quote in character literal */
char *s = "\""; /* quote in string literal */

char c = '''; /* invalid */
char *s = """; /* invalid */
Since you cannot have an empty character constant, ''' is not ambiguous, so
it could be allowed.

For the OP: now that you understand quoting issues better, how does C handle
triple quoting à la python:

char *s3 = """'""";

And what is wrong with these:

char c2 = '""';
char c3 = '"""';

--
Chqrlie.
Nov 26 '07 #8

P: n/a
Charlie Gordon wrote:
....
And what is wrong with these:

char c2 = '""';
char c3 = '"""';
Nothing, as far as I can see, though the value stored in c2 and c3 is
implementation-defined.
Nov 26 '07 #9

P: n/a
Charlie Gordon wrote:
[...]
Since you cannot have an empty character constant, ''' is not ambiguous, so
it could be allowed.
int ch = ''' + ''';

What value do you suggest ch should have? Twice the
value of '\'', or the implementation-defined value of a
character literal containing seven characters, or something
else?

--
Eric Sosman
es*****@ieee-dot-org.invalid
Nov 26 '07 #10

P: n/a
"Eric Sosman" <es*****@ieee-dot-org.invalida écrit dans le message de
news: Ac******************************@comcast.com...
Charlie Gordon wrote:
>[...]
Since you cannot have an empty character constant, ''' is not ambiguous,
so it could be allowed.

int ch = ''' + ''';

What value do you suggest ch should have? Twice the
value of '\'', or the implementation-defined value of a
character literal containing seven characters, or something
else?
Good point. Thus exits ''' for '\'';

But then why disallow the empty character constant ?
We could make the empty character constant have the value 0. That would
improve readability of code dealing with ends of strings:

if (str[i] == '') {
return i;
}

It would be somewhat consistent with the string literal syntax:

char *s = "";
assert(*s == '');

I'll wait till April 1st, 2008 to submit this one for consideration in C20XY

--
Chqrlie.
Nov 26 '07 #11

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