what's the difference between the next 2 declarations?

[Wade Yin]

Hi,

What's the difference between:

char *x="abcde";

and

char y[]={"abcde"};
I can't modify the value of the variable x in functions, but y can be do.

Is there any other similar problem need to be notice?

Thanks in advance!

Wade Yin

[Jack Klein]

On Mon, 5 Apr 2004 13:05:38 +0800, "Wade Yin" <li********@163 .com>
wrote in comp.lang.c:

Hi,

What's the difference between:

char *x="abcde";
x is a pointer to the a six character (including the '\0') string
literal. Attempting to modify a string literal causes undefined
behavior. x itself can be modified to point to a different array of
characters.
and

char y[]={"abcde"};
y is an array of 6 characters, initialized with the string literal.
The characters in y can be changed.
I can't modify the value of the variable x in functions, but y can be do.

Is there any other similar problem need to be notice?
No, the situation with string literals is a special case and there are
no others like it, except for wide string literals.
Thanks in advance!

Wade Yin

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
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alt.comp.lang.l earn.c-c++
http://www.contrib.andrew.cmu.edu/~a...FAQ-acllc.html

[Jack Klein]

On Mon, 5 Apr 2004 13:05:38 +0800, "Wade Yin" <li********@163 .com>
wrote in comp.lang.c:

Hi,

What's the difference between:

char *x="abcde";
x is a pointer to the a six character (including the '\0') string
literal. Attempting to modify a string literal causes undefined
behavior. x itself can be modified to point to a different array of
characters.
and

char y[]={"abcde"};
y is an array of 6 characters, initialized with the string literal.
The characters in y can be changed.
I can't modify the value of the variable x in functions, but y can be do.

Is there any other similar problem need to be notice?
No, the situation with string literals is a special case and there are
no others like it, except for wide string literals.
Thanks in advance!

Wade Yin

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.l earn.c-c++
http://www.contrib.andrew.cmu.edu/~a...FAQ-acllc.html

[Wade Yin]

"Jack Klein" <ja*******@spam cop.net>
??????:1l****** *************** ***********@4ax .com...

On Mon, 5 Apr 2004 13:05:38 +0800, "Wade Yin" <li********@163 .com>
wrote in comp.lang.c:

Hi,

What's the difference between:

char *x="abcde";
x is a pointer to the a six character (including the '\0') string
literal. Attempting to modify a string literal causes undefined
behavior. x itself can be modified to point to a different array of
characters.

How does "abcde" stored in memory? we can find x in memory, but we can't
operate it?

and

char y[]={"abcde"};

y is an array of 6 characters, initialized with the string literal.
The characters in y can be changed.

I can't modify the value of the variable x in functions, but y can be do.
Is there any other similar problem need to be notice?

No, the situation with string literals is a special case and there are
no others like it, except for wide string literals.

Thanks in advance!

Wade Yin

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.l earn.c-c++
http://www.contrib.andrew.cmu.edu/~a...FAQ-acllc.html

[Wade Yin]

"Jack Klein" <ja*******@spam cop.net>
??????:1l****** *************** ***********@4ax .com...

On Mon, 5 Apr 2004 13:05:38 +0800, "Wade Yin" <li********@163 .com>
wrote in comp.lang.c:

Hi,

What's the difference between:

char *x="abcde";
x is a pointer to the a six character (including the '\0') string
literal. Attempting to modify a string literal causes undefined
behavior. x itself can be modified to point to a different array of
characters.

How does "abcde" stored in memory? we can find x in memory, but we can't
operate it?

and

char y[]={"abcde"};

y is an array of 6 characters, initialized with the string literal.
The characters in y can be changed.

I can't modify the value of the variable x in functions, but y can be do.
Is there any other similar problem need to be notice?

No, the situation with string literals is a special case and there are
no others like it, except for wide string literals.

Thanks in advance!

Wade Yin

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.l earn.c-c++
http://www.contrib.andrew.cmu.edu/~a...FAQ-acllc.html

[John Tsiombikas (Nuclear / the Lab)]

Wade Yin wrote:

char *x="abcde";

x is a pointer to the a six character (including the '\0') string
literal. Attempting to modify a string literal causes undefined
behavior. x itself can be modified to point to a different array of
characters.

How does "abcde" stored in memory? we can find x in memory, but we can't
operate it?

Can't "change it", yes, the standard says that you cannot change a
string literal. The implementation has the freedom to place it in a
write-only protected memory segment, in ROM, or in fact anywhere it
desires. It may even put it exactly where it puts a modifiable character
array.

--
John Tsiombikas (Nuclear / the Lab)
nu*****@siggrap h.org
http://thelab.demoscene.gr/nuclear/

[John Tsiombikas (Nuclear / the Lab)]

Wade Yin wrote:

char *x="abcde";

x is a pointer to the a six character (including the '\0') string
literal. Attempting to modify a string literal causes undefined
behavior. x itself can be modified to point to a different array of
characters.

How does "abcde" stored in memory? we can find x in memory, but we can't
operate it?

Can't "change it", yes, the standard says that you cannot change a
string literal. The implementation has the freedom to place it in a
write-only protected memory segment, in ROM, or in fact anywhere it
desires. It may even put it exactly where it puts a modifiable character
array.

--
John Tsiombikas (Nuclear / the Lab)
nu*****@siggrap h.org
http://thelab.demoscene.gr/nuclear/

[Christopher Benson-Manica]

Wade Yin <li********@163 .com> spoke thus:

How does "abcde" stored in memory?
Exactly how is (I believe) up to the implementation, but commonly it
ends up in read-only memory.
we can find x in memory, but we can't operate it?

Not without bad things potentially happening - depending on the
implementation, attempting to access memory denoted as read-only can
cause your program to crash.

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[Christopher Benson-Manica]

Wade Yin <li********@163 .com> spoke thus:

How does "abcde" stored in memory?
Exactly how is (I believe) up to the implementation, but commonly it
ends up in read-only memory.
we can find x in memory, but we can't operate it?

Not without bad things potentially happening - depending on the
implementation, attempting to access memory denoted as read-only can
cause your program to crash.

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[Leor Zolman]

On Mon, 5 Apr 2004 13:36:27 +0800, "Wade Yin" <li********@163 .com> wrote:

"Jack Klein" <ja*******@spam cop.net>
??????:1l***** *************** ************@4a x.com...

On Mon, 5 Apr 2004 13:05:38 +0800, "Wade Yin" <li********@163 .com>
wrote in comp.lang.c:

> Hi,
>
> What's the difference between:
>
> char *x="abcde";

x is a pointer to the a six character (including the '\0') string
literal. Attempting to modify a string literal causes undefined
behavior. x itself can be modified to point to a different array of
characters.

How does "abcde" stored in memory? we can find x in memory, but we can't
operate it?

If you go to this page:
http://www.bdsoft.com/courses/cprog-details.html
and click on the "slides" link, slides #33-42 illustrate the different ways
in which your two constructs are stored in memory, and the sorts of things
you're permitted to do with them.

(Note to rest of group: I haven't updated this material since I began
hanging out in clc, so there are probably lots of nits to pick WRT saying
what's const and what's not, etc. Rest assured I'll go over the entire
/course/ before I ever actually teach it again....)
-leor

--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at:
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