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Hector
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 Posted: Sun Feb 22, 2004 11:00 am Post subject: STL string::resize question / proposal |
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I think that the class basic_string would benefit from a function
similar to resize but that would not overwrite whatever (garbage) was
in the buffer. Obviuosly, I don't know how to obtain such desired
result without a new function in the string class. Let us call xresize
to the ideal function that would allow us do the following:
std::string s;
unsigned int sz = SOME_VALUE;
s.reserve(sz);
if (s.capacity() >= sz) {
int newsize = WriteMaxNoOfChars(& s[0], sz);
s.xresize(newsize);
}
WriteMaxNoOfChars is any of those old functions that take the address
and size of a buffer and return the number of written characters. The
problem with using the current string::resize is that it would
overwrite whatever was in the buffer with the default character.
Does anybody know how to obtain such behaviour with current functions?
Note that I don't know the size of the written part beforehand, just
the size of the buffer.
If a new function with the behaviour of xresize is required, can
somebody pass along this request to the people who makes the
standards?
Greetings,
Hector C.
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Niklas Matthies
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| Posted: Sun Feb 22, 2004 5:25 pm Post subject: Re: STL string::resize question / proposal |
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On 2004-02-22 11:00, Hector wrote:
:
| Quote: | s.reserve(sz);
if (s.capacity() >= sz) {
int newsize = WriteMaxNoOfChars(& s[0], sz);
s.xresize(newsize);
}
WriteMaxNoOfChars is any of those old functions that take the address
and size of a buffer and return the number of written characters. The
problem with using the current string::resize is that it would
overwrite whatever was in the buffer with the default character.
Does anybody know how to obtain such behaviour with current functions?
Note that I don't know the size of the written part beforehand, just
the size of the buffer.
|
s.resize(sz);
int newsize = WriteMaxNoOfChars(& s[0], sz);
s.resize(newsize);
It's not optimally efficient, but that shouldn't make much of a
difference in practice.
-- Niklas Matthies
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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Ulrich Eckhardt
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| Posted: Sun Feb 22, 2004 5:27 pm Post subject: Re: STL string::resize question / proposal |
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Hector wrote:
| Quote: | I think that the class basic_string would benefit from a function
similar to resize but that would not overwrite whatever (garbage) was
in the buffer. Obviuosly, I don't know how to obtain such desired
result without a new function in the string class. Let us call xresize
to the ideal function that would allow us do the following:
std::string s;
unsigned int sz = SOME_VALUE;
s.reserve(sz);
if (s.capacity() >= sz) {
int newsize = WriteMaxNoOfChars(& s[0], sz);
s.xresize(newsize);
}
|
This doesn't necessarily work, string is not required to store its
characters in a contiguous array, IIRC. Also, your use of reserve() is not
guaranteed to work, I think.
Anyhow, I'd rather say that basic_string needs a function to create an
array of given size and return the pointer to it, for interfacing to
legacy C-functions. CString::GetBufferSetLength() comes to mind...
Uli
--
Questions ?
see C++-FAQ Lite: http://parashift.com/c++-faq-lite/ first !
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Dhruv Matani
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| Posted: Sun Feb 22, 2004 5:30 pm Post subject: Re: STL string::resize question / proposal |
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On Sun, 22 Feb 2004 06:00:53 -0500, Hector wrote:
| Quote: | I think that the class basic_string would benefit from a function
similar to resize but that would not overwrite whatever (garbage) was
in the buffer. Obviuosly, I don't know how to obtain such desired
result without a new function in the string class. Let us call xresize
to the ideal function that would allow us do the following:
|
Try string::reserve(...);
--
Regards,
-Dhruv.
Proud to be a Vegetarian.
http://www.vegetarianstarterkit.com/
http://www.vegkids.com/vegkids/index.html
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Andrei Alexandrescu
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| Posted: Mon Feb 23, 2004 11:37 am Post subject: Re: STL string::resize question / proposal |
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"Hector" <hhcalderon (AT) yahoo (DOT) com> wrote
| Quote: | I think that the class basic_string would benefit from a function
similar to resize but that would not overwrite whatever (garbage) was
in the buffer.
|
Indeed such a functionality would add string more efficient. The safe way to
do it, however, is to have basic_string define a resize() that takes a
function that will initialize the data:
template <class F>
void basic_string::resize_f(size_type s, F init);
During resizing, resize_f will call init(old_end, new_end) to initialize the
data. If a programmer is sure she wants to leave the data uninitialized,
then she passes a function that does nothing.
This way the STL remains as safe as the programmer using it wants.
Andrei
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Sergei Emantayev
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| Posted: Wed Mar 03, 2004 8:25 pm Post subject: Re: STL string::resize question / proposal |
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[email]hhcalderon (AT) yahoo (DOT) com[/email] (Hector) wrote in message news:<e64dc7b5.0402220018.4e557e9c (AT) posting (DOT) google.com>...
| Quote: | I think that the class basic_string would benefit from a function
similar to resize but that would not overwrite whatever (garbage) was
in the buffer. Obviuosly, I don't know how to obtain such desired
result without a new function in the string class. Let us call xresize
to the ideal function that would allow us do the following:
std::string s;
unsigned int sz = SOME_VALUE;
s.reserve(sz);
if (s.capacity() >= sz) {
int newsize = WriteMaxNoOfChars(& s[0], sz);
s.xresize(newsize);
}
|
Once you have used &s[0] (that may be unsupported by some STL providers),
you can also try the following trick. Note, it can slightly hit the performance.
s.assign(&s[0], newsize);
| Quote: |
Greetings,
Hector C.
|
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