From: Rodeo Red <rodeored AT netstep DOT net>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: compare()
Date: Thu, 02 Nov 2000 11:52:29 -0500
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To: djgpp AT delorie DOT com
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Steamer wrote:
> 
> Rodeo Red wrote:
> 
> > Now Ive got a similar problem with replace() and I don't know if this is
> > the same situation. How do I tell if my function is not supported ?
> 
> I'm not sure if there's a better way than simply trying it, or looking in
> the header files (c:\djgpp\lang\cxx).


Well I'll try, but since I easily get lost I'll describe the experience. 

I opened c:\djgpp\lang\cxx\string
which did not have the prototypes for compare or replace but it did have
#include <std/bastring.h>

So I opened c:\djgpp\lang\cxx\std\bastring.h and found this:


int compare (const basic_string& str, size_type pos = 0, size_type n =
npos) const;
  // There is no 'strncmp' equivalent for charT pointers.
  int compare (const charT* s, size_type pos, size_type n) const;
  int compare (const charT* s, size_type pos = 0) const
    { return compare (s, pos, traits::length (s)); } 

Only the last has an actual function. If these are the prototypes for
compare(), where are the actual functions for the first two ? In another
file I presume but I don't know where. 
  
Anyway, you posted 6 versions of compare, and there are three here, so
does that mean these three area the ones supported by djgpp ? 

> 
> > I'd like to be able to know, because if it is supported, the error is
> > probably mine.
> 
> I've downloaded Borland C++ 5.5, so I can always get a second opinion on
> the correctness of my code. 

Good idea- I actually have it too but had trouble getting it to work. 

> DJGPP is very good for C, but C++ is another
> matter - although things should change once GCC 3.0 appears and is ported
> to DJGPP.  (Borland's compiler is probably buggier than GCC, but its
> C++ library is currently more complete.)
> 
> > This is based on the example on page 1173 pf c++ Primer by Lippman and
> > Lajoie, a reliable text.
> 
> Not so reliable if this is a real example from the book...

> 
> > #include <string>
> > #include <algorithm>
> 
> You should have here:
> 
> #include <iostream>
> using namespace std;
> 
> > int main()
> > {
> >     string str = "The rain in Spain falls mainly on the plain\n";
> >     cout << "string:"<< str;
> >     string oldval = "rain";
> >     string newval = "sleet";
> >     replace (str.begin(), str.end(), oldval, newval) ;
> 
> This is incorrect.  The function std::replace() replaces elements,
> not sequences of elements.  For example:
> 
>     replace(str.begin(), str.end(), 'i', 'j');
> 
> This would replace every i in str by a j.
> 
> >     cout << "new str:"<< str;
> > }

-- 
I'm not sure what you mean by "sequence".  Do you mean you can't use a
string class object ? 
According to Lippman and Lajoie,  "replace() substitutes one or more
characters within a string with one or more alternative characters ".

Stroustrup says "Once a position is itentified, the value of individual
character positions can be changed using subscripting or whole
substrings can be replaced with new characters using replace().

basically I'd like to replace a character in a string with a second
string. I guess I have to use substr(), but it seems like the long way.  

In looking at the prototypes for replace(), I'm wondering what const
basic_string means.

red