What does this class do?

[desktop]

I found this class at:

http://www.icce.rug.nl/documents/cpl...7.html#FINDEND

class Twice
{
public:
bool operator()(size_t first, size_t second) const
{
return first == (second << 1);
}
};

it is used as the last argument to find_end() but I don't understand
what it does and why it is needed.

I have tried calling it with various integers but it always outputs 0:

Twice t = Twice();
bool t_bool = t.operator ()(4,8);
std::cout << t_bool << std::endl;

[red floyd]

desktop wrote:

I found this class at:

http://www.icce.rug.nl/documents/cpl...7.html#FINDEND

class Twice
{
public:
bool operator()(size_t first, size_t second) const
{
return first == (second << 1);
}
};

it is used as the last argument to find_end() but I don't understand
what it does and why it is needed.

I have tried calling it with various integers but it always outputs 0:

Twice t = Twice();
bool t_bool = t.operator ()(4,8);

t_bool = t(8,4); // should return true;

std::cout << t_bool << std::endl;

[Fei Liu]

desktop wrote:

I found this class at:

http://www.icce.rug.nl/documents/cpl...7.html#FINDEND

class Twice
{
public:
bool operator()(size_t first, size_t second) const
{
return first == (second << 1);
}
};

it is used as the last argument to find_end() but I don't understand
what it does and why it is needed.

I have tried calling it with various integers but it always outputs 0:

Twice t = Twice();
bool t_bool = t.operator ()(4,8);
std::cout << t_bool << std::endl;

Try this instead:

#include <iostream>
using namespace std;

class Twice
{
public:
bool operator()(size_t first, size_t second) const
{
return first == (second << 1);
}
};

int main(){
Twice t = Twice();
bool t_bool = t.operator ()(8, 4);
std::cout << t_bool << std::endl;
}

I suppose you need to look up how '<<' works.

[Jim Langston]

"desktop" <ff*@sss.comwrote in message
news:f0**********@news.net.uni-c.dk...

>I found this class at:

http://www.icce.rug.nl/documents/cpl...7.html#FINDEND

class Twice
{
public:
bool operator()(size_t first, size_t second) const
{
return first == (second << 1);
}
};

it is used as the last argument to find_end() but I don't understand what
it does and why it is needed.

I have tried calling it with various integers but it always outputs 0:

Twice t = Twice();
bool t_bool = t.operator ()(4,8);
std::cout << t_bool << std::end;

When you shift left by 1 (( << 1 )) you in effect mulitply times two. It
simply seems to be checking if the first parameter is twice the second. So
try with 8,4 since the second parm is being multiplied, not the first.

[Old Wolf]

On Apr 25, 9:26 am, desktop <[e-mail]:

I found this class at:

http://www.icce.rug.nl/documents/cpl...7.html#FINDEND

class Twice
{
public:
bool operator()(size_t first, size_t second) const
{
return first == (second << 1);
}
};

it is used as the last argument to find_end() but I don't understand
what it does and why it is needed.

It's an obfuscated way of writing:
bool Twice(size_t first, size_t second)
{
return first == second * 2;
}

I have tried calling it with various integers but it always outputs 0:

Twice t = Twice();
bool t_bool = t.operator ()(4,8);
std::cout << t_bool << std::endl;

Your code has a lot of redundancy:
Twice t;
std::cout << t(4,8) << std::endl;

or even:
std::cout << Twice()(4,8) << std::endl;

If you want to output 1 then pass in a first argument
that is twice the second one.