Reset a string?

[spike]

How do i reset a string?
I just want to empty it som that it does not contain any characters

Say it contains "hello world" at the time...
I want it to contain "". Nothing that is..

Thanx

[Leor Zolman]

On 5 Mar 2004 12:46:40 -0800, jo**@ljungh.se (spike) wrote:

How do i reset a string?
I just want to empty it som that it does not contain any characters

Say it contains "hello world" at the time...
I want it to contain "". Nothing that is..

Thanx

Easy: put a '\0' into the first position. Whether "s" is defined as a
pointer-to-char or an array-of-char, you just say:
*s = '\0';
or
s[0] = '\0';

But beware that is isn't a pointer-to-const-char; doing this may invoke
undefined behavior.

Also note that this doesn't "empty" the string, it just marks the first
position as the terminating NUL. The memory it was using is still there and
needs to be contended with.
-leor


Leor Zolman
BD Software
le**@bdsoft.com
www.bdsoft.com -- On-Site Training in C/C++, Java, Perl & Unix
C++ users: Download BD Software's free STL Error Message
Decryptor at www.bdsoft.com/tools/stlfilt.html

[Tor Husabø]

spike wrote:

How do i reset a string?
I just want to empty it som that it does not contain any characters

Say it contains "hello world" at the time...
I want it to contain "". Nothing that is..

char *str = "hello";
str[0] = '\0'; /* put a null terminator at the beginning */

Now the string is considered empty, and strlen(str) will return zero.

Tor

[Christopher Benson-Manica]

Tor Husabø <to***@student. hf.uio.no> spoke thus:

char *str = "hello";
str[0] = '\0'; /* put a null terminator at the beginning */

As Leor's post notes, this is incorrect code: str points to a string
literal, and thus may not be modified. You wanted something like

char str[]="hello";

--
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.

[Roberto Nunnari]

Tor Husabø wrote:

spike wrote:

How do i reset a string?
I just want to empty it som that it does not contain any characters

Say it contains "hello world" at the time...
I want it to contain "". Nothing that is..

char *str = "hello";
str[0] = '\0'; /* put a null terminator at the beginning */

be careful with char pointers like that.. it's not portable.
you have no garanties you'll be able to modify it like you did..
the compiler may put "hello" in readonly memory..

a correct version should be:

char str[] = "hello";
str[0] = '\0';

Best regards.
--
Roberto Nunnari -software engineer-
mailto:ro**@nun nisoft.ch
Residenza Boschetto 12 tel/fax: [phone]
6935 Bosco Luganese """ mobile: [phone]
Switzerland (o o)
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[Clark Cox]

In article <0O************ *******@news2.e .nsc.no>,
Tor Husabo <to***@student. hf.uio.no> wrote:

spike wrote:

How do i reset a string?
I just want to empty it som that it does not contain any characters

Say it contains "hello world" at the time...
I want it to contain "". Nothing that is..

char *str = "hello";
str[0] = '\0'; /* put a null terminator at the beginning */

That's undefined behavior, I bealieve that you meant (Notice the change
in the first line):

char str[] = "hello";
str[0] = '\0'; /* put a null terminator at the beginning */

[Eric Sosman]

Roberto Nunnari wrote:

Tor Husabø wrote:

spike wrote:

How do i reset a string?
I just want to empty it som that it does not contain any characters

Say it contains "hello world" at the time...
I want it to contain "". Nothing that is..

char *str = "hello";
str[0] = '\0'; /* put a null terminator at the beginning */

be careful with char pointers like that.. it's not portable.
you have no garanties you'll be able to modify it like you did..
the compiler may put "hello" in readonly memory..

Even if no read-only memory is involved you can find
yourself in trouble. For example,

char *str = "hello";
str[0] = '\0';
puts ("Some rhymes: bellow, fellow, Jell-O, and hello");

may well produce the output

Some rhymes: bellow, fellow, Jell-O, and

More than one compiler performs the optimization that
produces this effect when abused by incorrect code.

--
Er*********@sun .com

[CBFalconer]

Tor Husabø wrote:

spike wrote:

How do i reset a string? I just want to empty it som that it
does not contain any characters

Say it contains "hello world" at the time...
I want it to contain "". Nothing that is..

char *str = "hello";
str[0] = '\0'; /* put a null terminator at the beginning */

Now the string is considered empty, and strlen(str) will return
zero.

Nope. Now it has undefined (or possibly implementation defined)
behaviour, which may include going belly up. Think about it for a
while.

--
Chuck F (cb********@yah oo.com) (cb********@wor ldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE worldnet address!

[Jack Klein]

On Fri, 05 Mar 2004 22:12:15 +0100, Roberto Nunnari
<ro**@nunnisoft .ch> wrote in comp.lang.c:

Tor Husabø wrote:

spike wrote:

How do i reset a string?
I just want to empty it som that it does not contain any characters

Say it contains "hello world" at the time...
I want it to contain "". Nothing that is..

char *str = "hello";
str[0] = '\0'; /* put a null terminator at the beginning */

be careful with char pointers like that.. it's not portable.
you have no garanties you'll be able to modify it like you did..
the compiler may put "hello" in readonly memory..

a correct version should be:

char str[] = "hello";
str[0] = '\0';

Best regards.

It's more than not portable, it is undefined behavior.

The C standard (all versions) does not state that string literals are
read-only, or whether or not they may share storage. Attempting to
modify string literals in C is undefined behavior because the C
standard (all versions) specifically says it is.

--
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

[Tor Husabø]

CBFalconer wrote:

Tor Husabø wrote:

spike wrote:

How do i reset a string? I just want to empty it som that it
does not contain any characters

Say it contains "hello world" at the time...
I want it to contain "". Nothing that is..

char *str = "hello";
str[0] = '\0'; /* put a null terminator at the beginning */

Now the string is considered empty, and strlen(str) will return
zero.

Nope. Now it has undefined (or possibly implementation defined)
behaviour, which may include going belly up. Think about it for a
while.

I know, just hasn't written C code for a while.

Maybe I should blame the fact that the two declarations below are equal?
Maybe it's more confusing than really helpful to differentiate in this way?
void func1(int a[]); /* argument is pointer to array */
void func2(int *a); /* argument is pointer to a single int */

I guess this could be what had me fooled for a moment.