char* combination problem :(

[x]

Im trying to convert a few variables into a string object ( a
character string object). Only I have forgotten how! how
embarrasing....

char *x = (int1 + "/" + int2 + "/" + int3);

whats wrong? int1-3 can equal 0-99...




































6e

[Christopher Benson-Manica]

Re: char* combination problem :(

x <aotemp@hotmail .com> spoke thus:
[color=blue]
> Im trying to convert a few variables into a string object ( a
> character string object). Only I have forgotten how! how
> embarrasing....[/color]
[color=blue]
> char *x = (int1 + "/" + int2 + "/" + int3);[/color]
[color=blue]
> whats wrong? int1-3 can equal 0-99...[/color]

Simple - you forgot what language you were using. + isn't a catch-all
string creation operator in C++ like it is in various other languages.
If you want a string, declare a string. A decent C++ book and the FAQ
(posted below) will be most helpful.

http://www.slack.net/~shiva/welcome.txt

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

[color=blue]
> 6e[/color]

--
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.

[Rolf Magnus]

Re: char* combination problem :(

x wrote:
[color=blue]
> Im trying to convert a few variables into a string object ( a
> character string object). Only I have forgotten how! how
> embarrasing....
>
> char *x = (int1 + "/" + int2 + "/" + int3);
>
> whats wrong?[/color]

Doesn't make much sense to add integers and pointers together and write
the result into a pointer. Rembember: char* is not a string, but a
pointer to char. Try:

std::stringstre am stream;
stream << int1 << "/" << int2 << "/" << int3;
std::string x = stream.str();

[x]

Re: char* combination problem :(

Rolf Magnus <ramagnus@t-online.de> wrote in message news:<c5f1h1$51 c$03$1@news.t-online.com>...[color=blue]
> x wrote:
>[color=green]
> > Im trying to convert a few variables into a string object ( a
> > character string object). Only I have forgotten how! how
> > embarrasing....
> >
> > char *x = (int1 + "/" + int2 + "/" + int3);
> >
> > whats wrong?[/color]
>
> Doesn't make much sense to add integers and pointers together and write
> the result into a pointer. Rembember: char* is not a string, but a
> pointer to char. Try:
>
> std::stringstre am stream;
> stream << int1 << "/" << int2 << "/" << int3;
> std::string x = stream.str();[/color]


the only problem with that is that the function I am tryin to use the
string of characters with requires an input of char*......

[Christopher Benson-Manica]

Re: char* combination problem :(

x <aotemp@hotmail .com> spoke thus:
[color=blue]
> the only problem with that is that the function I am tryin to use the
> string of characters with requires an input of char*......[/color]

Still easy, if const char* is acceptable - std::string's c_str()
method converts the string to an array of characters, C-style. If you
need a non-const char *, then you'll have to declare an array of
characters and populate it appropriately (I suggest sprintf):

char buf[256]; // larger than required, just make sure it's big enough
// as sprintf will happily overflow the buffer if it
// isn't

sprintf( buf, "%d/%d/%d", int1, int2, int3 );

--
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.

[Bill Seurer]

Re: char* combination problem :(

x wrote:[color=blue]
> the only problem with that is that the function I am tryin to use the
> string of characters with requires an input of char*......[/color]

You can extract a char* from a string. See the functions in the string
class.

[Kevin Goodsell]

Re: char* combination problem :(

Christopher Benson-Manica wrote:[color=blue]
> x <aotemp@hotmail .com> spoke thus:
>
>[color=green]
>>the only problem with that is that the function I am tryin to use the
>>string of characters with requires an input of char*......[/color]
>
>
> Still easy, if const char* is acceptable - std::string's c_str()
> method converts the string to an array of characters, C-style. If you
> need a non-const char *, then you'll have to declare an array of
> characters and populate it appropriately (I suggest sprintf):
>
> char buf[256]; // larger than required, just make sure it's big enough
> // as sprintf will happily overflow the buffer if it
> // isn't
>
> sprintf( buf, "%d/%d/%d", int1, int2, int3 );
>[/color]

Or you could use Rolf's answer, and copy from the std::string into your
char array:

strcpy(buf, x.c_str()); // Be careful!!

Be sure to check the length first, and don't overflow buf. You could
even do this:

std::vector<cha r> vec_x(x.begin() , x.end());
vec_x.push_back ('\0');

// function that takes (non-const) char*:
SomeFunc(&vec_x[0]);


It occurs to me that a streambuf that writes to a std::vector<Cha rType>
could be useful in these cases -- you could skip creating a std::string
then copying it into a vector, and write into the vector in the first place.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

[Christopher Benson-Manica]

Re: char* combination problem :(

Kevin Goodsell <usenet2.spamfr ee.fusion@never box.com> spoke thus:
[color=blue]
> strcpy(buf, x.c_str()); // Be careful!![/color]

Or better,

strncpy( buf, sizeof buf - 1, x.c_str() );

although the vector solution is probably preferable. Nice one, btw.

--
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.

[Sam Dennis]

Re: char* combination problem :(

Christopher Benson-Manica wrote:[color=blue]
> Kevin Goodsell <usenet2.spamfr ee.fusion@never box.com> spoke thus:[color=green]
>> strcpy(buf, x.c_str()); // Be careful!![/color]
>
> Or better,
>
> strncpy( buf, sizeof buf - 1, x.c_str() );[/color]

That's not such a great idea if one is to do C-style string processing
on the result; strncpy doesn't guarantee null-termination. (Also, the
arguments are in the wrong order.)

If you must do this sort of thing in C++, this should be safe:

char buf[N];
*buf = 0;
strncat( buf, x.c_str(), sizeof buf - 1 );

--
++acr@,ka"

[Christopher Benson-Manica]

Re: char* combination problem :(

Sam Dennis <sam@malfunctio n.screaming.net > spoke thus:
[color=blue][color=green]
>> strncpy( buf, sizeof buf - 1, x.c_str() );[/color][/color]
[color=blue]
> That's not such a great idea if one is to do C-style string processing
> on the result; strncpy doesn't guarantee null-termination. (Also, the
> arguments are in the wrong order.)[/color]

Yikes, I can't believe I blew it on the argument order. Well,
actually I can... *sigh*

As far as null-termination goes, you're right in general - but when
strncpy is used intelligently (as I attempted to do, but failed...),
it does null-terminate the string.
[color=blue]
> If you must do this sort of thing in C++, this should be safe:[/color]
[color=blue]
> char buf[N];
> *buf = 0;
> strncat( buf, x.c_str(), sizeof buf - 1 );[/color]

Agreed.

--
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.