How to initialize a char*?

[Ioannis Vranos]

Re: How to initialize a char*?

"Christophe r Benson-Manica" <ataru@nospam.c yberspace.org> wrote in message
news:c5hbdn$e0l $1@chessie.cirr .com...[color=blue]
> Peter <ybi10@yahoo.co m> spoke thus:
>[color=green]
> > char* ptr;
> > func(..., ptr);[/color]
>
> This is bad - ptr is uninitialized (not even NULL), so passing it to a
> function is either pointless or an invitation to disaster, a mistake
> in any case.[/color]


Why?

[color=blue][color=green]
> > How to properly initialize a char*? I used to use[/color]
>[color=green]
> > char* ptr = "";[/color]
>
> Depends on what you're doing with it. You probably were told that
> because it should be
>
> const char *ptr="";[/color]


And what would be the use of that?


[color=blue]
> Why? Because "" is a constant empty string; trying to modify it
> invites disaster. Therefore, pointers to such string literals (so
> they're called) should be declared const; that way if you try to
> modify what it points to the compiler can inform you of your mistake.[/color]


The above is entirely, completely useless.






Ioannis Vranos

[Ioannis Vranos]

Re: How to initialize a char*?

"Julie" <julie@nospam.c om> wrote in message
news:407C4EE4.2 C85958D@nospam. com...[color=blue]
>
> Presume that func is declared as:
>
> void func(int input, char * & dest);[/color]


You can't do that!


[color=blue]
> Your statement may only be correct if func is declared as:
>
> void func(int input, char * dest);[/color]


I do not think his statement is correct.






Ioannis Vranos

[Ioannis Vranos]

Re: How to initialize a char*?

"Julie" <julie@nospam.c om> wrote in message
news:407C5EC1.D BCC116F@nospam. com...[color=blue]
>
> Here is another example that is perfectly legitimate:
>
> void func(char * const input, int word_number, char * & ptr_to_word);
> // find word in input and store address in ptr[/color]


I do not think it is. You can take references from pointers only in
templates. Even in this case passing an unitialised char * would not have
any bad effect by its own.


[color=blue]
> No allocations, no (thread-hostile???) static buffers, no overflow.
>[color=green]
> > It needs to be rewritten to use std::string.[/color]
>
> As I previously replied, char * is a perfectly legitimate and usable type.
> Blanket statements such as "use std::string" serve no purpose.
>
> The answer to the OP's question is simple and concise:
>
> Initialize a char * w/ NULL.[/color]


Nope. If he chooses to make the unneeded initialisation he should use 0, NOT
NULL.






Ioannis Vranos

[Julie]

Re: How to initialize a char*?

Ioannis Vranos wrote:[color=blue]
>
> "Julie" <julie@nospam.c om> wrote in message
> news:407C4EE4.2 C85958D@nospam. com...[color=green]
> >
> > Presume that func is declared as:
> >
> > void func(int input, char * & dest);[/color]
>
> You can't do that![/color]

???

Sure you can -- a reference to a variable of type char *.
[color=blue][color=green]
> > Your statement may only be correct if func is declared as:
> >
> > void func(int input, char * dest);[/color]
>
> I do not think his statement is correct.[/color]

I do not understand what your point is. To whom are you referring to by "his"?

[David Harmon]

Re: How to initialize a char*?

On Tue, 13 Apr 2004 15:47:58 -0700 in comp.lang.c++, Julie
<julie@nospam.c om> wrote,[color=blue]
>Yes, my statement was directed at the 'evil' part -- there is nothing 'evil'
>about it, it just has the potential to lead to undefined behavior.[/color]

This issue is covered in Marshall Cline's C++ FAQ. See the topic
"[6.14] What does the FAQ mean by "such-in-such is evil"?".

http://www.parashift.com/c++-faq-lite/

[Ioannis Vranos]

Re: How to initialize a char*?

"Julie" <julie@nospam.c om> wrote in message
news:407C758E.8 D10840@nospam.c om...[color=blue]
> Ioannis Vranos wrote:[color=green]
> >
> > "Julie" <julie@nospam.c om> wrote in message
> > news:407C4EE4.2 C85958D@nospam. com...[color=darkred]
> > >
> > > Presume that func is declared as:
> > >
> > > void func(int input, char * & dest);[/color]
> >
> > You can't do that![/color]
>
> ???
>
> Sure you can -- a reference to a variable of type char *.
>[color=green][color=darkred]
> > > Your statement may only be correct if func is declared as:
> > >
> > > void func(int input, char * dest);[/color]
> >
> > I do not think his statement is correct.[/color]
>
> I do not understand what your point is. To whom are you referring to by[/color]
"his"?


Can you provide a working example with a main() using such a function
accepting char * &?






Ioannis Vranos

[Ioannis Vranos]

Re: How to initialize a char*?

"Matt Wharton" <no_matt_wharto n@agilent.com_s pam> wrote in message
news:1081894795 .688751@cswreg. cos.agilent.com ...[color=blue]
>
> This is true, but I think it would be fair to argue that it is always good
> practice to initialize variables to something (most likely NULL or 0 in[/color]
this[color=blue]
> case). No harm comes from doing this (always initializing), whereas there
> are many situations where NOT initializing will shoot you in the foot.[/color]


An example?

To make long things short, initialization doesn't protect you from anything.
The only thing that it could "protect you" in theory is in the call of
delete/delete[] family to an ititialised-to-0 pointer. In reality however
such a call occurs at the end of a process and you will have done more
things previously by mistake on that 0 initialised pointer (e.g.
dereferencing it) that would be equally disastrous/undefined.

Initialisation does not protect you from any mistake.






Ioannis Vranos

[Ioannis Vranos]

Re: How to initialize a char*?

"Julie" <julie@nospam.c om> wrote in message
news:407C6E1E.1 7403F38@nospam. com...[color=blue]
>
> Absolutely, variables, as a general rule, should be initialized to a
> standardized default value.[/color]

Not absolutely.






Ioannis Vranos

[Ioannis Vranos]

Re: How to initialize a char*?

"Kevin Goodsell" <usenet2.spamfr ee.fusion@never box.com> wrote in message
news:s_Xec.8580 $A_4.7680@newsr ead1.news.pas.e arthlink.net...[color=blue]
>
> Never use any variable before you've given it a meaningful value. Doing
> so gives undefined behavior, and could crash your program or worse.[/color]

You reminded me a humorous text that i had read a long ago which i just
searched in google. Check it:

http://www.lysator.liu.se/c/ten-commandments.html

Of course it has nothing to do with the subject, but this "never" of yours
reminded it to me. :-)


[color=blue]
> This uses a dangerous and deprecated language feature -- the implicit
> conversion of a string literal to a (non-const) char*. I'd suggest
> making your compiler warn about this if it provides such a warning.[/color]

Eh?

[color=blue]
> Initialize it with whatever you need. You're the only one who knows what
> purpose it serves, so we can't suggest what to use. But leaving it
> uninitialized is an error, and doesn't make sense.[/color]

It is not an error!






Ioannis Vranos

[Julie]

Re: How to initialize a char*?

Ioannis Vranos wrote:[color=blue]
>
> "Julie" <julie@nospam.c om> wrote in message
> news:407C5EC1.D BCC116F@nospam. com...[color=green]
> >
> > Here is another example that is perfectly legitimate:
> >
> > void func(char * const input, int word_number, char * & ptr_to_word);
> > // find word in input and store address in ptr[/color]
>
> I do not think it is. You can take references from pointers only in
> templates. Even in this case passing an unitialised char * would not have
> any bad effect by its own.[/color]

Reference to a pointer type is perfectly legal, and has nothing to do w/
templates.

If you feel that I'm wrong, please correct me by referencing the C++ standard.
[color=blue][color=green]
> > No allocations, no (thread-hostile???) static buffers, no overflow.
> >[color=darkred]
> > > It needs to be rewritten to use std::string.[/color]
> >
> > As I previously replied, char * is a perfectly legitimate and usable type.
> > Blanket statements such as "use std::string" serve no purpose.
> >
> > The answer to the OP's question is simple and concise:
> >
> > Initialize a char * w/ NULL.[/color]
>
> Nope. If he chooses to make the unneeded initialisation he should use 0, NOT
> NULL.[/color]

NULL is perfectly acceptable, and is standard.

[Julie]

Re: How to initialize a char*?

Ioannis Vranos wrote:[color=blue]
> Can you provide a working example with a main() using such a function
> accepting char * &?[/color]

How about you go ahead and try it, and learn for yourself.

[Julie]

Re: How to initialize a char*?

David Harmon wrote:[color=blue]
>
> On Tue, 13 Apr 2004 15:47:58 -0700 in comp.lang.c++, Julie
> <julie@nospam.c om> wrote,[color=green]
> >Yes, my statement was directed at the 'evil' part -- there is nothing 'evil'
> >about it, it just has the potential to lead to undefined behavior.[/color]
>
> This issue is covered in Marshall Cline's C++ FAQ. See the topic
> "[6.14] What does the FAQ mean by "such-in-such is evil"?".
> http://www.parashift.com/c++-faq-lite/[/color]

Thanks for pointing it out.

After reading, that section definitely comes off as infantile and
inappropriate. I'd much prefer a more precise (and less humanity-subjective)
term as 'evil'. But I didn't write that FAQ, nor have any plans to write one,
so MC is free to write what he wants. Regardless, that doesn't preclude me
from stating that 'evil' is a poor word choice when discussing programmatic
constructs and behaviors.

[Julie]

Re: How to initialize a char*?

Ioannis Vranos wrote:[color=blue]
>
> "Julie" <julie@nospam.c om> wrote in message
> news:407C6E1E.1 7403F38@nospam. com...[color=green]
> >
> > Absolutely, variables, as a general rule, should be initialized to a
> > standardized default value.[/color]
>
> Not absolutely.[/color]

Yes absolutely.

From now on, in order to be considered a productive participant, you may want
to include more than simple phrase answers and actually provide some insight
into the matter.

[Ioannis Vranos]

Re: How to initialize a char*?

"Julie" <julie@nospam.c om> wrote in message
news:407C7FDE.A EB6117@nospam.c om...[color=blue]
> Ioannis Vranos wrote:[color=green]
> > Can you provide a working example with a main() using such a function
> > accepting char * &?[/color]
>
> How about you go ahead and try it, and learn for yourself.[/color]


Why don't you try? Just provide an empty definition of a function getting
char *&), create a main() with a valid call to it and if it compiles post it
here (i am not kidding you will see).






Regards,

Ioannis Vranos

[Julie]

Re: How to initialize a char*?

Ioannis Vranos wrote:[color=blue]
>
> "Matt Wharton" <no_matt_wharto n@agilent.com_s pam> wrote in message
> news:1081894795 .688751@cswreg. cos.agilent.com ...[color=green]
> >
> > This is true, but I think it would be fair to argue that it is always good
> > practice to initialize variables to something (most likely NULL or 0 in[/color]
> this[color=green]
> > case). No harm comes from doing this (always initializing), whereas there
> > are many situations where NOT initializing will shoot you in the foot.[/color]
>
> An example?
>
> To make long things short, initialization doesn't protect you from anything.
> The only thing that it could "protect you" in theory is in the call of
> delete/delete[] family to an ititialised-to-0 pointer. In reality however
> such a call occurs at the end of a process and you will have done more
> things previously by mistake on that 0 initialised pointer (e.g.
> dereferencing it) that would be equally disastrous/undefined.
>
> Initialisation does not protect you from any mistake.[/color]

That is true.

Perhaps it would be better to term this as 'zero initialization' , after all

char * ptr = (char *)12345;

is initialized, but not much better than leaving it uninitialized.