<string> class with support of Null-Bytes?

[Karl Ebener]

Hi!

I asked a similar question before but then changed everything to using
char-Arrays instead of the string class, but I would rather not do this
again.

So, does anyone know of a string-Class similar to the STL-<string> that
supports null-bytes?

I tried with standard <string> but this definitely does not support
them... :(

Tnx
Karl

[Alf P. Steinbach]

Re: &lt;string&g t; class with support of Null-Bytes?

* Karl Ebener:[color=blue]
>
> I asked a similar question before but then changed everything to using
> char-Arrays instead of the string class, but I would rather not do this
> again.
>
> So, does anyone know of a string-Class similar to the STL-<string> that
> supports null-bytes?
>
> I tried with standard <string> but this definitely does not support
> them... :([/color]

Depends what you mean by "support", but with usual definitions that's
not correct.

Perhaps post a simple program that shows what you mean by "not support"?

Then we can see whether the problem is in the code or with std::string,
and give better suggestions on how to proceeed.

--
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?

[Karl Ebener]

Re: &lt;string&g t; class with support of Null-Bytes?

Little change:
[color=blue]
> I tried with standard <string> but this definitely does not support
> them... :([/color]

-> I tried using length()-method which stops at null-bytes and c_str()
of course extracts only part till null-byte.
Have I only not seen any possibility to extract the content as char* ?

Tnx
Karl

[Alf P. Steinbach]

Re: &lt;string&g t; class with support of Null-Bytes?

* Karl Ebener:[color=blue]
> Little change:
>[color=green]
> > I tried with standard <string> but this definitely does not support
> > them... :([/color]
>
> -> I tried using length()-method which stops at null-bytes[/color]

It doesn't.

[color=blue]
> and c_str() of course extracts only part till null-byte.[/color]

It doesn't, see §21.3.6/1.

[color=blue]
> Have I only not seen any possibility to extract the content as char* ?[/color]

Post some code.

--
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?

[Karl Ebener]

Re: &lt;string&g t; class with support of Null-Bytes?

Alf P. Steinbach schrieb:[color=blue]
> Depends what you mean by "support", but with usual definitions that's
> not correct.
>
> Perhaps post a simple program that shows what you mean by "not support"?
>
> Then we can see whether the problem is in the code or with std::string,
> and give better suggestions on how to proceeed.
>[/color]
Okay, this is my test program.
What I want to do finally, is read a complete (binary) file into a
string and then send this via using socket to/from server.
I am using socket-routines that use strings because it is much easier
this way and I would love to leave it at that and not recode everything...

Tnx
Karl

#include <string>
#include <iostream>

using namespace std;

int main()
{
string abc = "abc\0abc\0 "; // string contains Null-bytes
cout << abc << ":" << abc.length() << endl; // output is: 3
FILE* fp;

fp = fopen("ABC", "w");
fwrite(abc.c_st r(), 8, 1, fp); // file will contain: "abc" and Garbage
fclose(fp);
}

[Rolf Magnus]

Re: &lt;string&g t; class with support of Null-Bytes?

Karl Ebener wrote:
[color=blue]
> Alf P. Steinbach schrieb:[color=green]
>> Depends what you mean by "support", but with usual definitions that's
>> not correct.
>>
>> Perhaps post a simple program that shows what you mean by "not support"?
>>
>> Then we can see whether the problem is in the code or with std::string,
>> and give better suggestions on how to proceeed.
>>[/color]
> Okay, this is my test program.
> What I want to do finally, is read a complete (binary) file into a
> string and then send this via using socket to/from server.
> I am using socket-routines that use strings because it is much easier
> this way and I would love to leave it at that and not recode everything...
>
> Tnx
> Karl
>
> #include <string>
> #include <iostream>
>
> using namespace std;
>
> int main()
> {
> string abc = "abc\0abc\0 "; // string contains Null-bytes[/color]

No. Your literal contains 0-bytes. The conversion constructor from C style
strings to std::string of course has to stop at \0, since that's the value
that marks the end of a C style string. Try:

const char c[] = "abc\0abc\0 ";

string abc(c, sizeof(c));

This tells the constructor to not stop at \0, but read the specified number
of characters.
[color=blue]
> cout << abc << ":" << abc.length() << endl; // output is: 3[/color]

That's because only the first 3 characters were actually copied into the
string.
[color=blue]
> FILE* fp;
>
> fp = fopen("ABC", "w");
> fwrite(abc.c_st r(), 8, 1, fp); // file will contain: "abc" and Garbage[/color]

Again, that's because the string only contains the first 3 characters.
[color=blue]
> fclose(fp);
> }[/color]

[Alf P. Steinbach]

Re: &lt;string&g t; class with support of Null-Bytes?

* Karl Ebener:[color=blue]
>
> #include <string>
> #include <iostream>
>
> using namespace std;
>
> int main()
> {
> string abc = "abc\0abc\0 "; // string contains Null-bytes
> cout << abc << ":" << abc.length() << endl; // output is: 3
> FILE* fp;
>
> fp = fopen("ABC", "w");
> fwrite(abc.c_st r(), 8, 1, fp); // file will contain: "abc" and Garbage
> fclose(fp);
> }[/color]

The problem in the abc declaration is that you invoke the constructor
that takes a C string as argument, and by definition that C string ends
at the first nullbyte.

Try


#include <string>
#include <iostream>

#define ELEMCOUNT( array ) (sizeof(array)/sizeof(*array))

int main()
{
static char const abc_data[] = "abc\0abc\0 ";
std::string abc( abc_data, ELEMCOUNT( abc_data );

std::cout << abc << ":" << abc.length() << std::endl;
}

But you might instead (for efficiency) want to use std::vector<cha r>.

Also, the file should be opened in binary mode.

--
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?

[Dimitris Kamenopoulos]

Re: &lt;string&g t; class with support of Null-Bytes?

Karl Ebener wrote:
[color=blue]
> Okay, this is my test program.[/color]

My guess is that std::string's functions (including constructors) that take
a C-Style string as an argument, *do* treat it as a C-style (i.e.
null-terminated) string.

Makes sense, doesn't it? You don't want

char s[15] = "sth";
string s1(s);

to allocate 11 extra null characters in s1 for no reason :-)

If, OTOH, you put a '\0' in an std::string, it will not be treated as a
terminating character.

Check out this example to see what I mean:

#include <iostream>
#include <string>

int main(){
std::string s("abc\0abc\0") ;
std::cout<<s.le ngth()<<std::en dl; //prints 3, not 9
std::string s2;
s2.push_back('a ');
s2.push_back('\ 0');
s2.push_back('b ');
std::cout<<s2.l ength()<<std::e ndl; //prints 3, not 1
}


Note: c_string() will return a const char *, which means that the string
returned will always stop at the first null byte, for any code that cares
about it (e.g. strlen or strcpy). Better use a vector<char> if you want
byte semantics.

[Dave O'Hearn]

Re: &lt;string&g t; class with support of Null-Bytes?

Karl Ebener wrote:[color=blue]
> fwrite(abc.c_st r(), 8, 1, fp); // file will contain: "abc"
> // and Garbage[/color]

As a separate issue, data() would be better than c_str() here. c_str()
may expand the string's internal buffer, to make room for an extra null
character past the end. You don't need a null-terminated C-string to
call fwrite, so you can just use data().

--
Dave O'Hearn

[Rolf Magnus]

Re: &lt;string&g t; class with support of Null-Bytes?

Dimitris Kamenopoulos wrote:
[color=blue]
> Karl Ebener wrote:
>[color=green]
>> Okay, this is my test program.[/color]
>
> My guess is that std::string's functions (including constructors) that
> take a C-Style string as an argument, *do* treat it as a C-style (i.e.
> null-terminated) string.
>
> Makes sense, doesn't it? You don't want
>
> char s[15] = "sth";
> string s1(s);
>
> to allocate 11 extra null characters in s1 for no reason :-)[/color]

That's not the main point. The constructor takes a pointer, which doesn't
contain any information about the size of the array pointed to. So the \0
is the _only_ way at all to know where a C style string ends.

[Paul]

Re: &lt;string&g t; class with support of Null-Bytes?


"Karl Ebener" <myonlyb@vollbi o.de> wrote in message
news:41bec2d2$0 $29843$9b4e6d93 @newsread2.arco r-online.net...[color=blue]
> Little change:
>[color=green]
> > I tried with standard <string> but this definitely does not support
> > them... :([/color]
>
> -> I tried using length()-method which stops at null-bytes and c_str()
> of course extracts only part till null-byte.[/color]

What you are saying is totally false. std::string fully supports strings
with embedded NULLs. You just need to know the functions to use.

First, use the right constructor. The std::string has a few constructors --
a good C++ book that goes into the standard library will show you the
various constructors. The proper constructor is the one that takes a const
char * and an integer denoting the number of characters.

#include <string>
std::string s("abc\0123", 7);

Second, use the std::string::da ta( ) member function instead of
std::string::c_ str(). This respects the length of the string and does not
terminate on the first NULL.

Third, if you need to add binary data to a std::string, use the append( )
function. If you need to reassign binary data, use the
std::string::ap pend() on an empty string, or the std::string::as sign( )
member function.

Paul

[Ron Natalie]

Re: &lt;string&g t; class with support of Null-Bytes?

Karl Ebener wrote:[color=blue]
> Little change:
>[color=green]
>> I tried with standard <string> but this definitely does not support
>> them... :([/color]
>
>
> -> I tried using length()-method which stops at null-bytes and c_str()
> of course extracts only part till null-byte.
> Have I only not seen any possibility to extract the content as char* ?[/color]

Multibyte does not contain nulls. I'm confused as what you are asking.
Neither c_str() nor length() cares anything about embedded nulls.

Now that being said, there is NO real multibyte handling in std::string
either.

[Ron Natalie]

Re: &lt;string&g t; class with support of Null-Bytes?

Karl Ebener wrote:
[color=blue]
> So, does anyone know of a string-Class similar to the STL-<string> that
> supports null-bytes?[/color]

std:string handles null bytes just fine. The only thing that you have to
be careful with is that if you use the conversions to/from char*, you need
to pass/retrieve the actual length because the default strlen() calculations
won't work.

std::string s;
s.push_back('a' );
s.push_back('\0 ');
s.push_back('\b ');

cout << s.size(); // prints 3
const char* cp = s.c_str();

cout << cp[0] << cp[2]; // prints ab

[Old Wolf]

Re: &lt;string&g t; class with support of Null-Bytes?

Paul wrote:[color=blue]
> "Karl Ebener" <myonlyb@vollbi o.de> wrote:
>
> #include <string>
> std::string s("abc\0123", 7);[/color]

Undefined behaviour. "abc\0123" is an array of 6 chars:
{'a', 'b', 'c', '\012', '3', '\0'}
[color=blue]
> Second, use the std::string::da ta( ) member function instead of
> std::string::c_ str(). This respects the length of the string
> and does not terminate on the first NULL.[/color]

std::string::c_ str() does not terminate on the first null
character. The only difference between c_str() and data()
is that c_str() appends a null character.

std::string s("abc\0def", 7);
std::cout << (s.c_str() + 4) << std::endl;

will output "def".
BTW, the macro NULL is not really relevant to null characters.

[Old Wolf]

Re: &lt;string&g t; class with support of Null-Bytes?

Paul wrote:[color=blue]
> "Karl Ebener" <myonlyb@vollbi o.de> wrote:
>
> #include <string>
> std::string s("abc\0123", 7);[/color]

Undefined behaviour. "abc\0123" is an array of 6 chars:
{'a', 'b', 'c', '\012', '3', '\0'}
[color=blue]
> Second, use the std::string::da ta( ) member function instead of
> std::string::c_ str(). This respects the length of the string
> and does not terminate on the first NULL.[/color]

std::string::c_ str() does not terminate on the first null
character. The only difference between c_str() and data()
is that c_str() appends a null character.

std::string s("abc\0def", 7);
std::cout << (s.c_str() + 4) << std::endl;

will output "def".
BTW, the macro NULL is not really relevant to null characters.