How can I insert null bytes in to std::string?

[Pep]

I have to interface to an older library that uses strings and there is
no alternative. I need to pass a string that is padded with null
bytes. So how can I append these null bytes to the std::string?

Yes I know it would be better to use something like a vector but I do
not have that option.

Yes I know that I will not be able to use std::string.c_s tr() but will
instead have to use std:;string.get Data().

TIA.

[fungus]

Pep wrote:

>
Yes but it was suggested to me that there was a way that did not
involve using append, so as I could not find any way I decided to ask
if anyone knew of one of those "tricks".

Doing anything outside of the standard wouldn't
be a "trick" it would be "undefined behaviour".

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[Daniel T.]

In article <11************ **********@h48g 2000cwc.googleg roups.com>,
"Pep" <pe**********@y ahoo.co.ukwrote :

Victor Bazarov wrote:

Pep wrote:

I have to interface to an older library that uses strings and there is
no alternative. I need to pass a string that is padded with null
bytes. So how can I append these null bytes to the std::string?

Probably using "append" member... Have you RTFM?

Yes but it was suggested to me that there was a way that did not
involve using append, so as I could not find any way I decided to ask
if anyone knew of one of those "tricks".

Guess it will have to be append then.

Well, you could always do: "myString[pos] = 0" if you know that pos is a
valid position.

[Ivan Vecerina]

"Pep" <pe**********@y ahoo.co.ukwrote in message
news:11******** **************@ h48g2000cwc.goo glegroups.com.. .
:
: Victor Bazarov wrote:
: Pep wrote:
: I have to interface to an older library that uses strings and there
is
: no alternative. I need to pass a string that is padded with null
: bytes. So how can I append these null bytes to the std::string?
: >
: Probably using "append" member... Have you RTFM?
: >
:
: Yes but it was suggested to me that there was a way that did not
: involve using append, so as I could not find any way I decided to ask
: if anyone knew of one of those "tricks".
:
: Guess it will have to be append then.

And what's wrong with it ?
s.append( 5, '\0' ); // appends five NULs, pretty straightforward ?

: Yes I know it would be better to use something like a vector but I
do
: not have that option.
: >
: In your case it probably does not matter. Why do you think that
'vector'
: has any advantage?
:
: I read something in a previous posting that suggested vectors would be
: better though as you, I do not understand how other than perhaps the
: poster meant that you should not in theory have nulls in strings.

Vector historically had to be used if you wanted write
access *and* contiguous storage (because only .data()
and .c_str() were guaranteed to return a pointer to
contiguous storage, and the returned buffer is *const*).

But using &s[0] has always worked in practice,
and the standard has been revised to allow this
[ contiguity is now always guaranteed ]
: Yes I know that I will not be able to use std::string.c_s tr() but
will
: instead have to use std:;string.get Data().
..c_str() might have an advantage over .data() in your case:
it will append an additional NULL char to the returned buffer ;)
Cheers --Ivan
--
http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form

[Pep]

peter koch wrote:

<snip>

>
This is not true - sort of anyway:

char const* weird_hello = "Weird \0hello";

does contain an embedded null and if'd call it a C-string you surely
are wrong! ;-)
I've seen a list of lines being defined with a \0 separating each
string and using an empty string as a terminator. Something like 'H'
'e' 'l' 'l' 'o' 0 'W' 'o' 'r' 'l' 'd' '!' 0 0.

My guess is the OP wanted to have two nulls at the end of the string-
Another possibility is that the interface expects the string in a
fixed-length buffer and the buffer to be containing zeroes at the end
of the string. You believe I'm kidding, but I've actually witnessed
such an interface once.

Correct. I have taken over a large legacy system a long time ago and
still have not got to grips completely with it. The previous
programmers, all juniors, have coded a method that only caters for
strings and yet we need to send binary data through it now. You would
think that a hex encoder/decoder would deal with binary data wouldn't
you?

So without going to the lengths of changing millions of lines of code,
it would have been nice to send binary data in the string and let the
latest method in the encoder, which deals with char* arrays, to handle
it.

In the end I got completely pissed off and spent an extra 2 days
writing a proper encoder and then updating the massive code deck to
accommodate it. Now it all works correctly, encoding from binary to
string and decoding form string to binary :)

<snip>