Converting to using templates

[tech]

Hi, i have the following design issue. In our app we use different
codecs to encode/decode packets of data
I have defined a base codec class as follows

class CCodec
{
public:
CCodec() {};
virtual ~CCodec(){};

virtual unsigned char Encode(short ibuf ) = 0;

virtual short Decode(unsigned char ibuf) = 0;
};

std::vector<unsigned charm_SendBuffer; // defined in Voip class

bool Voip::SendData(signed short* buf, size_t size)
{
for(int i = 0; i != ENC_BUF_LEN; ++i)
{
SendBuffer[i] = m_codec->Encode(buf[i]); // m_Codec points to
concrete implementation
}

// then SendDataToNetwork(SendBuffer)

}

ENC_BUF_LEN = size of the SendBuffer vector

What i need to do is send a packet of data to the network in the
SendData function
which is given some data, i've got type short above but it could be
any type ie char, long etc

the Encode function takes a short and returns a char (as thats what
compression does) however
as we will support different codecs the signature of this function
could vary, it would probably always
return a char but its input parameter could vary like with Send data.

The above is hardcoded to use shorts but i need something generic ,
can this be done with templates
some how?

[Noah Roberts]

tech wrote:

Hi, i have the following design issue. In our app we use different
codecs to encode/decode packets of data
I have defined a base codec class as follows

class CCodec
{
public:
CCodec() {};
virtual ~CCodec(){};

virtual unsigned char Encode(short ibuf ) = 0;

virtual short Decode(unsigned char ibuf) = 0;
};

std::vector<unsigned charm_SendBuffer; // defined in Voip class

bool Voip::SendData(signed short* buf, size_t size)
{
for(int i = 0; i != ENC_BUF_LEN; ++i)
{
SendBuffer[i] = m_codec->Encode(buf[i]); // m_Codec points to
concrete implementation
}

// then SendDataToNetwork(SendBuffer)

}

ENC_BUF_LEN = size of the SendBuffer vector

What i need to do is send a packet of data to the network in the
SendData function
which is given some data, i've got type short above but it could be
any type ie char, long etc

the Encode function takes a short and returns a char (as thats what
compression does) however
as we will support different codecs the signature of this function
could vary, it would probably always
return a char but its input parameter could vary like with Send data.

The above is hardcoded to use shorts but i need something generic ,
can this be done with templates
some how?

What you seem to be saying is that SendData could have data other than
shorts and that the codec thing could be the same.

template< typename T >
bool SendData(T * buf, size_t s)
{
....buffer[i] = encode->Encode(buf[i]);
}

Same with CCodec except your encoder is probably going to have to work
with sizeof(T) instead of whatever hard coded value you have in there.

There are actually numerous options for doing the CCodec class,
including having it, itself be a template, its function Encode be a
template, or Encode being overridden per type.

This seem pretty basic, so maybe I don't understand the question.

[tech]

Thanks, but how i can have a virtual template Encode function

for example i have the following G711 concrete implmentation

unsigned char CG711ULAW::Encode(signed short data )
{
return linear2ulaw(data);
}

i can't do this can i?
template<typename T>
virtual unsigned char Encode(T ibuf ) = 0;

[Noah Roberts]

tech wrote:

Thanks, but how i can have a virtual template Encode function

for example i have the following G711 concrete implmentation

unsigned char CG711ULAW::Encode(signed short data )
{
return linear2ulaw(data);
}

i can't do this can i?
template<typename T>
virtual unsigned char Encode(T ibuf ) = 0;

Right, you can't do that.

You either have to make your class hierarchy templated, or you'll need
to make Encode functions for all types that might go through the
SendData function. You'll want to enforce that with some kind of
metafunction and boost::enable_if, if possible (you're not constrained,
as I once was, from using boost).

You could look up "Non-Virtual Interface" too...I don't know what help
it will offer.

A templated class structure would look like so:

template < typename T >
class Top
{
public:
unsigned char(T elem) const = 0;
// this function is probably not changing the class? const
}:

template < typename T >
class Bottom : public Top<T>
{
public:
unsigned char(T elem) const { ...implement...}
};

There are other, more complex structures I can think of that could solve
problems like this, but in the end it's something you need to do
specific to your needs. So look into the above, NVI, and possibly the
curiously reoccurring template pattern as tools that you could build a
solution from.