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Alexandros
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 Posted: Sat Dec 27, 2003 11:59 am Post subject: char* to vector<bool> |
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Hi. How can I create a vector<bool> efficiently from a char* or a
vector<char> ?
For example, if char* c[2] == (8,10) I want vector<bool> v to be:
(0000100000001010)
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Alexandros
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| Posted: Sat Dec 27, 2003 12:13 pm Post subject: Re: char* to vector<bool> |
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Alexandros escribió:
| Quote: | Hi. How can I create a vector<bool> efficiently from a char* or a
vector<char> ?
For example, if char* c[2] == (8,10) I want vector<bool> v to be:
(0000100000001010)
|
It would be enough to be able to get access to each bit of the byte
vector, without creating a vector<bool>. I'd like the most efficient
solution.
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Victor Bazarov
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| Posted: Sat Dec 27, 2003 4:03 pm Post subject: Re: char* to vector<bool> |
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"Alexandros" <email (AT) company (DOT) com> wrote...
| Quote: | Alexandros escribió:
Hi. How can I create a vector<bool> efficiently from a char* or a
vector<char> ?
For example, if char* c[2] == (8,10) I want vector<bool> v to be:
(0000100000001010)
It would be enough to be able to get access to each bit of the byte
vector, without creating a vector<bool>. I'd like the most efficient
solution.
|
Wrap your char array in a class with a special member function to
access those bits:
class MyVectorBool {
int size;
unsigned char *storage;
public:
MyVectorBool(const char* str)
: size(strlen(str))
, storage(new char[size+1])
{
std::copy(str, str + size + 1, storage);
}
// don't forget the other three: d-tor, copy c-tor, assignment op.
bool get_bit(std::size_t n) const
{
unsigned char which_bit = 1 << (n % CHAR_BIT);
return storage[n / CHAR_BIT] & which_bit;
}
void set_bit(std::size_t n, bool towhat)
{
...
}
void clear_bit(std::size_t n)
{
...
}
};
Should be efficient enough...
Victor
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Martijn Lievaart
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| Posted: Tue Dec 30, 2003 4:01 pm Post subject: Re: char* to vector<bool> |
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On Sat, 27 Dec 2003 12:13:15 +0000, Alexandros wrote:
| Quote: | Alexandros escribió:
Hi. How can I create a vector<bool> efficiently from a char* or a
vector<char> ?
For example, if char* c[2] == (8,10) I want vector<bool> v to be:
(0000100000001010)
It would be enough to be able to get access to each bit of the byte
vector, without creating a vector<bool>. I'd like the most efficient
solution.
|
Efficient in what? Memory? Lookup time? Programmer time? These are
almost orthogonal quantities for this problem.
And are you sure you need the most efficient solution? On todays hardware
a few cycles and/or bytes are hardly noticed, if at all.
I personally would use a std::bitset if the size is known beforehand. If
not, I might have a look at vector<bool>, but as that has many
limitations, I would also look if a vector<char> (wrapped in a suitable
class) would be acceptable. Also a set<bool> might be acceptable, if only
a few bits are set it might even be very efficient.
Back to your original problem. A vector<bool> has the problem that it does
not resize on access through [], so either resize it on every setting of a
bit, or find the maximum value in c and resize to that maximum. From there
it is a simple loop (or for_each with a suitable functor) to set each bit.
HTH,
M4
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