opposite of c_str() ??
Allan Bruce
I can use c_str() to convert from a string to a char array. How do I do the
opposite?
Thanks
Allan
Ivan Vecerina
news:3e5f619e$0$5362$cc9e...@news.dial.pipex.com...
| I can use c_str() to convert from a string to a char array. How do I do
the
| opposite?
If cstr is a pointer to a null-terminated C string, you can construct
an std::string from it.
For example:
return str::string( cstr );
One caveat: cstr must not be a NULL pointer (or behavior will be undefined).
I hope this helps,
--
Ivan Vecerina, Dr. med. <> http://www.post1.com/~ivec
Soft Dev Manger, xitact <> http://www.xitact.com
Brainbench MVP for C++ <> http://www.brainbench.com
Dean Kutryk
This worked for me:
#include<iostream>
#include<string>
int main() {
char phrase[] = "Hello ";
std::string s (phrase);
std::cout << s << std::endl;
return 0;
}
Gianni Mariani
> Allan Bruce wrote:
>
>> Hi there,
>> I can use c_str() to convert from a string to a char array. How do I
>> do the
>> opposite?
>> Thanks
>> Allan
>>
>
>
> This worked for me:
>
> #include<iostream>
> #include<string>
>
> int main() {
>
> char phrase[] = "Hello ";
>
> std::string s (phrase);
This is better.
std::string s (phrase, sizeof(phrase) -1);
For the purpose of this discussion, you're 100% correct, I'm just
pointing out a source of inefficiency I see all too often.
Homer Meyer
"Gianni Mariani" <gii_...@mariani.ws> wrote in message
news:3E5F8055...@mariani.ws...
Have you timed it? How much less efficient is it really? Does this kind of
thing really make a critical difference in the speed of your code?
Kevin Goodsell
Assign it.
std::string str;
str = "this is a string";
-Kevin
Neil Butterworth
"Kevin Goodsell" <good...@bridgernet.com> wrote in message
news:podv5vofglvvr75un...@4ax.com...
Why assign it? why not use the constructor?
std::string str( "this is a string" );
NeilB
Nikhil Tiwari
but I know that there certainly are instances when the assignment
operator and the constructor behave differently...
Nikhil
"Neil Butterworth" <neil_but...@lineone.net> wrote in message news:<3e5fba61$1...@mk-nntp-1.news.uk.worldonline.com>...
Neil Butterworth
"Nikhil Tiwari" <nikhil...@hotmail.com> wrote in message
news:cf059008.03022...@posting.google.com...
>
> "Neil Butterworth" <neil_but...@lineone.net> wrote in message
news:<3e5fba61$1...@mk-nntp-1.news.uk.worldonline.com>...
> > "Kevin Goodsell" <good...@bridgernet.com> wrote in message
> > news:podv5vofglvvr75un...@4ax.com...
> > > On Fri, 28 Feb 2003 13:18:20 -0000, "Allan Bruce"
> > > <all...@REMOVEdsl.pipex.com> wrote:
> > >
> > > >Hi there,
> > > >I can use c_str() to convert from a string to a char array. How do I
do
> > the
> > > >opposite?
> > > >Thanks
> > > >Allan
> > > >
> > >
> > > Assign it.
> > >
> > > std::string str;
> > > str = "this is a string";
> >
> > Why assign it? why not use the constructor?
> >
> > std::string str( "this is a string" );
> >
Please don't top post - rearranged:
> Quite honestly, I'm not sure if it makes a difference in this case,
If you are not sure, then why share your uncertainty with us? I am sure taht
it makes a difference.
> but I know that there certainly are instances when the assignment
> operator and the constructor behave differently...
They behave differently in _all_ circumstances.
NeilB
Alan Krueger
news:3E5F8055...@mariani.ws...
> Dean Kutryk wrote:
> > int main() {
> >
> > char phrase[] = "Hello ";
> >
> > std::string s (phrase);
>
> This is better.
> std::string s (phrase, sizeof(phrase) -1);
>
> For the purpose of this discussion, you're 100% correct, I'm just
> pointing out a source of inefficiency I see all too often.
...which will fail as soon as someone makes this kind of change:
int main()
{
// ...
// search argv for index of phrase
// ...
char* phrase = argv[index];
std::string s( phrase, sizeof(phrase) - 1 );
// ...
}
Either comment the heck out of that efficiency decision, or use the one that
works in either case. Even though you understand it, you might not notice
it the next time you work on that code, or some C++ newbie will be assigned
to maintain your code and not notice it.
Gianni Mariani
8 seconds vs 23 seconds .... you guess which one takes longer !
#include <string>
char foo[16384]; // if this is 16 bytes there is still a 30% delta
std::string maker1()
{
return std::string( foo, sizeof(foo) -1 );
}
std::string maker2()
{
return std::string( foo );
}
int main()
{
for ( int i = 0; i < sizeof( foo ) -1; i ++ )
{
foo[i] = 'A';
}
for ( int j = 0; j < 1200000; j ++ )
{
maker2();
}
return 0;
}
Julián Albo
> #include <string>
>
> char foo[16384]; // if this is 16 bytes there is still a 30% delta
>
> std::string maker1()
> {
> return std::string( foo, sizeof(foo) -1 );
> }
>
> std::string maker2()
> {
> return std::string( foo );
> }
>
> int main()
> {
> for ( int i = 0; i < sizeof( foo ) -1; i ++ )
> {
> foo[i] = 'A';
> }
You don't zero terminate foo.
Regards.
Fraser Ross
> an std::string from it.
> For example:
> return str::string( cstr );
>
> One caveat: cstr must not be a NULL pointer (or behavior will be
undefined).
Use the range constructor if the array is not null terminated.
std::string(cstr, cstr+size_of_cstr);
Fraser.
Gianni Mariani
Yes I do ! This behaviour is well defined.
Regards
G
Ron Natalie
"Fraser Ross" <fraserATmembers.v21.co.uk> wrote in message news:3e5f...@news.greennet.net...
He was talking about cstr == NULL, not the string containing it
having a null.