Using std::string

[Victor Hannak]

I am taking a program written in Borland C++ Builder 4 and converting the
non-GUI related code to be generic c++ that can run anywhere. My main issue
at this point is dealing with the string classes used in this program. All
strings in this program are of the Borland AnsiString class. I would like
to convert them over to use std::string.

In order to keep from breaking the original program, I was hoping to use
std::string everywhere except the GUI class. In the GUI class (which is
still a BCB4 GUI), I was hoping to do some translation from std::string to
AnsiString to maintain compatibility with the visual components.

So 2 questions:

1) When moving a string from the std::string datatype to the AnsiString
datatype, is the only way to do it to copy character by character from one
datatype to the other? (I have never used the std::string class before)

2) Throughout the code, there are AnsiString variables declared with the
keyword "String". Is there a way I can set up an alias so that anytime the
compiler sees "String", it uses the std::string class (i.e. "string"
lower-case) instead? (I think the operators/methods are pretty much
compatible between the two, but correct me if I am wrong)

Thanks,

Vic

[Victor Hannak]

Also, how do I convert other data types like floats to std::string. Using
the BCB AnsiString class, it was as simple as:

float tmp = 5.0;
String MyString = String(tmp);

This would result in:

MyString == "5.0"

If anyone knows of a good reference where I can find this kind of info,
please point me in that direction, but I could not find much on the web.

Thanks

[jeffc]

"Victor Hannak" <vi***********@ nospam.kodak.co m> wrote in message
news:bj******** **@news.kodak.c om...

1) When moving a string from the std::string datatype to the AnsiString
datatype, is the only way to do it to copy character by character from one
datatype to the other? (I have never used the std::string class before)
If you look at the interface for string, and understand the interface to
AnsiString, I think you'll find something fairly easy.

2) Throughout the code, there are AnsiString variables declared with the
keyword "String". Is there a way I can set up an alias so that anytime the compiler sees "String", it uses the std::string class (i.e. "string"
lower-case) instead? (I think the operators/methods are pretty much
compatible between the two, but correct me if I am wrong)

I don't know, because I've never used AnsiString. But "typedef" will
probably do what you want.

[John Harrison]

"Victor Hannak" <vi***********@ nospam.kodak.co m> wrote in message
news:bj******** **@news.kodak.c om...

Also, how do I convert other data types like floats to std::string. Using
the BCB AnsiString class, it was as simple as:

float tmp = 5.0;
String MyString = String(tmp);

This would result in:

MyString == "5.0"

Use an ostringstream for this kind of conversion.

float tmp = 5.0;
ostringstream oss;
oss << tmp;
string my_string = oss.str();
If anyone knows of a good reference where I can find this kind of info,
please point me in that direction, but I could not find much on the web.

Thanks

http://www.dinkumware.com/refxcpp.html

john

[Mike Wahler]

Victor Hannak <vi***********@ nospam.kodak.co m> wrote in message
news:bj******** **@news.kodak.c om...

Also, how do I convert other data types like floats to std::string. Using
the BCB AnsiString class, it was as simple as:

float tmp = 5.0;
String MyString = String(tmp);

This would result in:

MyString == "5.0"

If anyone knows of a good reference where I can find this kind of info,
please point me in that direction, but I could not find much on the web.

You'll need books. See www.accu.org for peer reviews.

About your question: you can use a stringstream to
do the conversion:

float f(3.14);
std::istringstr eam iss;
iss >> f;
std::string s(iss.str());
std::cout << s << '\n'; /* prints 3.14 */

The best reference I know of for the C++
standard library is: www.josuttis.com/libbook

-Mike

[Ron Natalie]

"Mike Wahler" <mk******@mkwah ler.net> wrote in message news:4i******** *********@newsr ead4.news.pas.e arthlink.net...

std::istringstr eam iss;
iss >> f;

The above fails (backwards from what the user wanted anyhow)
std::ostringstr eam oss;
oss << f;

[Rolf Magnus]

Victor Hannak wrote:

I am taking a program written in Borland C++ Builder 4 and converting
the non-GUI related code to be generic c++ that can run anywhere. My
main issue at this point is dealing with the string classes used in
this program.
All strings in this program are of the Borland AnsiString class. I
would like to convert them over to use std::string.

In order to keep from breaking the original program, I was hoping to
use std::string everywhere except the GUI class. In the GUI class
(which is still a BCB4 GUI), I was hoping to do some translation from
std::string to AnsiString to maintain compatibility with the visual
components.

So 2 questions:

1) When moving a string from the std::string datatype to the
AnsiString datatype, is the only way to do it to copy character by
character from one datatype to the other? (I have never used the
std::string class before)
Most people here probably have never used the AnsiString class.

2) Throughout the code, there are AnsiString variables declared with
the
keyword "String". Is there a way I can set up an alias so that
anytime the
compiler sees "String", it uses the std::string class (i.e. "string"
lower-case) instead? (I think the operators/methods are pretty much
compatible between the two, but correct me if I am wrong)

You can use a typedef:

typedef std::string String;

[Peter Koch Larsen]

"Victor Hannak" <vi***********@ nospam.kodak.co m> skrev i en meddelelse
news:bj******** **@news.kodak.c om...

Also, how do I convert other data types like floats to std::string. Using
the BCB AnsiString class, it was as simple as:

float tmp = 5.0;
String MyString = String(tmp);

This would result in:

MyString == "5.0"

If anyone knows of a good reference where I can find this kind of info,
please point me in that direction, but I could not find much on the web.

Thanks

As John Harrison and Mike Wahler have already pointed out, the stringstream
is often the way to go, but you might also want to have a look at boost,
where there is a function lexical cast. Using boost, converting is as simple
as:

MyString = lexical_cast< std::string >(tmp);

The downside is that you can't controle the precise formatting (number of
decimals and stuff like that) with lexical_cast... . here a stringstream is
still the way to go.

Kind regards
Peter

[Victor Hannak]

> Use an ostringstream for this kind of conversion.

float tmp = 5.0;
ostringstream oss;
oss << tmp;
string my_string = oss.str();

Great suggestions...t hat's exactly the info I needed... but one more
question...

I have taken the above code and made it into a function:

string str(float In) {
ostrstream oss;
oss << In;
return(oss.str( ));
}

This way, I can do something like:

float Success = 95.5;
WriteGUI("succe ss = " + str(Success).su bstr(0,3) + "%");

Where WriteGUI() is my own function that writes something to the GUI (this
is where I convert it back to AnsiString as described in my previous post).

So I _could_ replicate/overload the str() function for each type of data
that I would want to potentially print out. But is there a way to make it
generic so that it doesn't matter what data type I am passing in? (Since
ultimately it is limited to what ostrstream can accept)

Vic

[Dave Vandervies]

In article <bj**********@n ews.kodak.com>,
Victor Hannak <vi***********@ nospam.kodak.co m> wrote:

string str(float In) {
ostrstream oss;
oss << In;
return(oss.str( ));
}
[...]
So I _could_ replicate/overload the str() function for each type of data
that I would want to potentially print out. But is there a way to make it
generic so that it doesn't matter what data type I am passing in? (Since
ultimately it is limited to what ostrstream can accept)

This looks to me like a good place for a template:

template <class T> std::string str(T in)
{
ostringstream os;
os<<in;
return os.str();
}

/*Use like this:*/
WriteGUI("An int: "+str(my_in t));
WriteGUI("A double: "+str(my_double ));
WriteGUI("A user-defined type: "+str(my_user_d efined_type));
I'd probably try inlining it, too, though I'm not sure that would make
a noticeable difference in either speed or size.
dave
(Still working on the jump from C to C++, so any comments on my code
would be welcome)

--
Dave Vandervies dj******@csclub .uwaterloo.ca
[Y]ou can write bad code that just barely works in both languages, or good
code that works only in one language -- so pick one, and write good code in
that language. --Chris Torek in comp.lang.c (crossposted to comp.lang.c++)