how to avoid reinterpret_cas t in this snippet?

[KK]

Hello all,
I have a unsigned char buffer 'buffer[1024]' and I need to convert the
first 12 bytes of it into a string. Below is a code that should work,
however, how can I avoid reinterpret_cas t operator?
Or Is there a simple way to get around this?
Thanks.
-KK
/* not tested yet */
typedef unsigned char BYTE
std::string GetStringFromBy teBuffer(const BYTE* const buffer, int pos )
{
const char *chAry = reinterpret_cas t <const char *> (buffer + pos);
std::string tmp(chAry,12);
return chAry;
}

[Alf P. Steinbach]

* ro**********@gm ail.com:

Actually it is pretty obvious that std::string has no constructor that
takes unsigned char* as an argument just by looking at its
constructors... none of them take an unsigned char* as an argument. The
fact that you can pass one as an argument to some of these constructors
is a consequence of a language feature, mainly that it will
automatically do some conversions for you. The very important
distinction here is that unsigned char* is being converted to something
else,

No, it isn't.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Bob Hairgrove]

On Fri, 02 Dec 2005 09:05:31 -0500, Kai-Uwe Bux <jk********@gmx .net>
wrote:

The following
*does* compile:

// test_uchar.cpp

#include <iostream>
#include <ostream>
#include <string>

int main()
{
const unsigned char msg[] = "Hello";
std::string s( msg, msg+5 );
std::cout << s << std::endl;
}

Not on my machine:

Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
test_uchar.cpp:
Turbo Incremental Link 5.00 Copyright (c) 1997, 2000 Borland
Error: Unresolved external 'std::basic_str ing<char,
std::char_trait s<char>, std::allocator< char> >::basic_string <char,
std::char_trait s<char>, std::allocator< char> >(const unsigned char *,
const unsigned char *, const std::allocator< char>&)' referenced from
E:\TEST_UCHAR.O BJ

--
Bob Hairgrove
No**********@Ho me.com

[Bob Hairgrove]

On 2 Dec 2005 05:23:54 -0800, Mi************* @tomtom.com wrote:

Nope. However, this does:

#include <string>
const unsigned char msg[] = "Hello";
std::string s(msg,msg+sizeo f(msg));

Not on my machine:

Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
test_uchar.cpp:
Turbo Incremental Link 5.00 Copyright (c) 1997, 2000 Borland
Error: Unresolved external 'std::basic_str ing<char,
std::char_trait s<char>, std::allocator< char> >::basic_string <char,
std::char_trait s<char>, std::allocator< char> >(const unsigned char *,
const unsigned char *, const std::allocator< char>&)
' referenced from E:\TEST_UCHAR.O BJ

--
Bob Hairgrove
No**********@Ho me.com

[Bob Hairgrove]

On Sun, 04 Dec 2005 22:48:59 +0100, Bob Hairgrove
<in*****@bigfoo t.com> wrote:

On Fri, 02 Dec 2005 09:05:31 -0500, Kai-Uwe Bux <jk********@gmx .net>
wrote:

The following
*does* compile:

// test_uchar.cpp

#include <iostream>
#include <ostream>
#include <string>

int main()
{
const unsigned char msg[] = "Hello";
std::string s( msg, msg+5 );
std::cout << s << std::endl;
}

Not on my machine:

Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
test_uchar.cpp :
Turbo Incremental Link 5.00 Copyright (c) 1997, 2000 Borland
Error: Unresolved external 'std::basic_str ing<char,
std::char_trai ts<char>, std::allocator< char> >::basic_string <char,
std::char_trai ts<char>, std::allocator< char> >(const unsigned char *,
const unsigned char *, const std::allocator< char>&)' referenced from
E:\TEST_UCHAR. OBJ

OK -- it compiles, but it doesn't link because Borland provides no
*compiler magic* to make it work.

--
Bob Hairgrove
No**********@Ho me.com

[Bob Hairgrove]

On Sun, 04 Dec 2005 22:49:59 +0100, Bob Hairgrove
<in*****@bigfoo t.com> wrote:

On 2 Dec 2005 05:23:54 -0800, Mi************* @tomtom.com wrote:

Nope. However, this does:

#include <string>
const unsigned char msg[] = "Hello";
std::string s(msg,msg+sizeo f(msg));

Not on my machine:

Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
test_uchar.cpp :
Turbo Incremental Link 5.00 Copyright (c) 1997, 2000 Borland
Error: Unresolved external 'std::basic_str ing<char,
std::char_trai ts<char>, std::allocator< char> >::basic_string <char,
std::char_trai ts<char>, std::allocator< char> >(const unsigned char *,
const unsigned char *, const std::allocator< char>&)
' referenced from E:\TEST_UCHAR.O BJ

OK -- it compiles, but it doesn't link because Borland provides no
*compiler magic* to make it work.

--
Bob Hairgrove
No**********@Ho me.com

[Kai-Uwe Bux]

Ron Natalie wrote:

Kai-Uwe Bux wrote:

Bob Hairgrove wrote:

On Fri, 02 Dec 2005 09:58:35 GMT, al***@start.no (Alf P. Steinbach)
wrote:

> Since char and unsigned char are different types, you must use either
> a C-style cast or reinterpret_cas t, as you have done. There is really
> no way to avoid it if you must pass unsigned char to this function.
You're the second person to state that so I'm interesting in the
reeasoning.
The reason? Because std::string has no constructor that takes unsigned
char* as an argument.
Hm, std::string has a templated constructor:
template<class InputIterator>
basic_string(In putIterator begin, InputIterator end,
const Allocator& a = Allocator());
Since unsigned char is convertible to char, this constructor should
match.

There is no coinstructor that takes ONLY an unsigned char* and an
integral value. He passed a unsigned char* and the integer 12.

True, but utterly irrelevant:

May I remind you of the original post:
I have a unsigned char buffer 'buffer[1024]' and I need to convert the
first 12 bytes of it into a string. Below is a code that should work,
however, how can I avoid reinterpret_cas t operator?
Or Is there a simple way to get around this?
Thanks.
-KK
/* not tested yet */
typedef unsigned char BYTE
std::string GetStringFromBy teBuffer(const BYTE* const buffer, int pos )
{
const char *chAry = reinterpret_cas t <const char *> (buffer + pos); std::string tmp(chAry,12);
return chAry;
}

The operative phrase being "*how* can I avoid...", the OP asks about a way
to implement GetStringFromBu ffer that avoids casts. This clearly can be
done using the templated std::string constructor I mentioned. The following
solution is essentially stolen from Alf Steinbach's post:

std::string GetStringFromBy teBuffer(const BYTE* const buffer, int pos )
{
return std::string( buffer+pos, buffer+pos+12 );
}

This fits the specs given by the OP. The claim that "there is really no way
to avoid it [casting] if you must pass unsigned char to this function" is
therefore false. The line "Because std::string has no constructor that
takes unsigned char* as an argument" was given as a reason, and since it
tries to argue something false, it is false itself or fails to imply what
it is supposed to argue. Make your pick: if you read it as narrow as

std::string ( unsigned char*, int ) is not valid

then it fails to imply what it is supposed to argue; if you use a broader
reading, the statement will become false.
Best

Kai-Uwe Bux

[Alf P. Steinbach]

* Bob Hairgrove:

On Sun, 04 Dec 2005 22:49:59 +0100, Bob Hairgrove
<in*****@bigfoo t.com> wrote:

On 2 Dec 2005 05:23:54 -0800, Mi************* @tomtom.com wrote:

Nope. However, this does:

#include <string>
const unsigned char msg[] = "Hello";
std::string s(msg,msg+sizeo f(msg));

Not on my machine:

Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
test_uchar.cpp :
Turbo Incremental Link 5.00 Copyright (c) 1997, 2000 Borland
Error: Unresolved external 'std::basic_str ing<char,
std::char_trai ts<char>, std::allocator< char> >::basic_string <char,
std::char_trai ts<char>, std::allocator< char> >(const unsigned char *,
const unsigned char *, const std::allocator< char>&)
' referenced from E:\TEST_UCHAR.O BJ

OK -- it compiles, but it doesn't link because Borland provides no
*compiler magic* to make it work.

Try

bcc32 -D"_RWSTD_COMPIL E_INSTANTIATE" -w-ccc -w-rch test_uchar.cpp

Hth.,

- Alf
PS: I recommend using some other free compiler, e.g. g++ or MSVC; <url:
http://home.no.net/dubjai/win32cpptut/html/w32cpptut_01_01 _02.html>.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Old Wolf]

Bob Hairgrove wrote:

Mi************* @tomtom.com wrote:

#include <string>
const unsigned char msg[] = "Hello";
std::string s(msg,msg+sizeo f(msg));

Not on my machine:

Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
test_uchar.cpp:
Turbo Incremental Link 5.00 Copyright (c) 1997, 2000 Borland
Error: Unresolved external 'std::basic_str ing<char,
std::char_trait s<char>, std::allocator< char> >::basic_string <char,
std::char_trait s<char>, std::allocator< char> >(const unsigned char *,
const unsigned char *, const std::allocator< char>&)

That's a bug in the standard library supplied with Borland C++.
The body of the constructor is never defined.
My workaround is to avoid using that constructor.

[Alf P. Steinbach]

* Old Wolf:

Bob Hairgrove wrote:

Mi************* @tomtom.com wrote:

#include <string>
const unsigned char msg[] = "Hello";
std::string s(msg,msg+sizeo f(msg));

Not on my machine:

Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
test_uchar.cpp:
Turbo Incremental Link 5.00 Copyright (c) 1997, 2000 Borland
Error: Unresolved external 'std::basic_str ing<char,
std::char_trait s<char>, std::allocator< char> >::basic_string <char,
std::char_trait s<char>, std::allocator< char> >(const unsigned char *,
const unsigned char *, const std::allocator< char>&)

That's a bug in the standard library supplied with Borland C++.
The body of the constructor is never defined.
My workaround is to avoid using that constructor.

See my reply to the same posting -- the constructor body is defined in
a file that is conditionally included by <string>.

I suspect there is also a way to link a compiled version of that file,
using some language extension (doing the job of 'export'), but, it's an
old compiler, so I don't care to use the time to find out.

Cheers,

- Alf

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Bob Hairgrove]

On Mon, 05 Dec 2005 01:06:01 GMT, al***@start.no (Alf P. Steinbach)
wrote:

Try

bcc32 -D"_RWSTD_COMPIL E_INSTANTIATE" -w-ccc -w-rch test_uchar.cpp

Hth.,

No, it doesn't really "help" (HTH == "hope this helps") <g>

The basic question remains:
Is it *required* by the C++ standard that your code compiles (and
links)? And if you think so, please explain why (and not just: "it
does").

[I hope you realize that the above "hack" can create serious problems
with code that is distributed among different DLLs which rely on
things defined in the DLLs supplied by Borland (e.g., anything even
remotely depending on VCL)?]

--
Bob Hairgrove
No**********@Ho me.com