Passing bitset to function

[Michal Wyrebski]

Hello,

I was thinking how is the fastest and the best way of passing bitset
variable to some function.
Only one method came to my mind. It's about passing converted value:

#v+
void func(unsigned long UL) {
bitset<8> B(UL);
cout << "B: " << B << endl;
}

int main() {
bitset<8> H('A');
func(H.to_ulong() );
return 0;
}
#v-

Of course converting to string is also possible.

OK this just works. But what if I want to pass some number of bits and
func() had no information about its number?
It's impossible to write like that:

#v+
void func(unsigned long UL, const int len) {
bitset<len> B(UL);
(...)
#v-

g++ says: `len' cannot appear in a constant-expression

How, then, pass some number of bits, that function could create
stucture (bitset) of required length?
Any ideas?
Michal

[Ali Çehreli]

"Michal Wyrebski" <mi*******@gmail.com> wrote in message
news:11**********************@z14g2000cwz.googlegr oups.com...

I was thinking how is the fastest and the best way of passing bitset
variable to some function.

Best way is probably passing by reference. Very common... To determine
whether it's the fastest, you will need to test different approaches in your
program.

#include <iostream>
#include <bitset>

typedef std::bitset<8> EightBits;

void func(EightBits const & bits)
{
std::cout << bits << '\n';
}

int main()
{
EightBits h('A');
func(h);
}

Ali

[John Harrison]

Michal Wyrebski wrote:

Hello,

I was thinking how is the fastest and the best way of passing bitset
variable to some function.
Only one method came to my mind. It's about passing converted value:

#v+
void func(unsigned long UL) {
bitset<8> B(UL);
cout << "B: " << B << endl;
}

int main() {
bitset<8> H('A');
func(H.to_ulong() );
return 0;
}
#v-

Of course converting to string is also possible.

OK this just works. But what if I want to pass some number of bits and
func() had no information about its number?
It's impossible to write like that:

#v+
void func(unsigned long UL, const int len) {
bitset<len> B(UL);
(...)
#v-

g++ says: `len' cannot appear in a constant-expression

How, then, pass some number of bits, that function could create
stucture (bitset) of required length?
Cannot be done, because bitset is a template the size must be a compile
time constant.
Any ideas?

If you need a set of bits whose size is not determined at compile time
then vector<bool>, vector<char> and string are all possiblities.
vector<bool> is specialised to take the minimum possible space (i.e.
several bits are stored as a single byte).

john