array of functions?

[Youssef Mesri]

I want to do something like this:


// declare a vector of type function
vector<(*foo)()> function_table;
//where
void foo()
{
do something
}
the above syntax isn't correct. How can I do it correctly?
thanks in advance for your answers.
Yous.

[mlimber]

Youssef Mesri wrote:

I want to do something like this:


// declare a vector of type function
vector<(*foo)()> function_table;
//where
void foo()
{
do something
}
the above syntax isn't correct. How can I do it correctly?
thanks in advance for your answers.
Yous.

#include <vector>
using namespace std;

void Foo1() {}
void Foo2() {}

int main()
{
typedef void (*pfn)();
vector<pfn> fns;
fns.push_back( Foo1 );
fns.push_back( Foo2 );
fns[0]();
return 0;
}

Cheers! --M

[Luke Meyers]

> vector<(*foo)()> function_table;

vector<return_type (*)(arg1_type, arg2_type)> function_table;

It's easier on everyone if you use a typedef, btw.

Luke

[Earl Purple]

Youssef Mesri wrote:

I want to do something like this:
// declare a vector of type function
vector<(*foo)()> function_table;
//where
void foo()
{
do something
}
the above syntax isn't correct. How can I do it correctly?

You need a return type.

But I'd advise against doing it. Use instead a vector of pointers to a
base-class. Then invoke a virtual function of that base-class.

(Commonly this is the solution to calling a function based on a value
passed in at run time. Often the collection used is a map).

[Youssef Mesri]

Earl Purple wrote:

Youssef Mesri wrote:

I want to do something like this:
// declare a vector of type function
vector<(*foo)()> function_table;
//where
void foo()
{
do something
}
the above syntax isn't correct. How can I do it correctly?

You need a return type.

But I'd advise against doing it. Use instead a vector of pointers to a
base-class. Then invoke a virtual function of that base-class.

(Commonly this is the solution to calling a function based on a value
passed in at run time. Often the collection used is a map).

I'm intersting to see an example prototype for this. can you please show
me an example.
thanks a lot
yous

[Clark S. Cox III]

On 2006-01-03 12:17:11 -0500, "Earl Purple" <ea********@gmail.com> said:

Youssef Mesri wrote:

I want to do something like this:
// declare a vector of type function
vector<(*foo)()> function_table;
//where
void foo()
{
do something
}
the above syntax isn't correct. How can I do it correctly?

You need a return type.

But I'd advise against doing it. Use instead a vector of pointers to a
base-class. Then invoke a virtual function of that base-class.

But then, you have to worry about managing the lifetime of the
pointed-to objects. If one were to simply store pointers to functions
in the container, then that issue goes away.
--
Clark S. Cox, III
cl*******@gmail.com

[Earl Purple]

I'm intersting to see an example prototype for this. can you please show
me an example.
thanks a lot
yous

A very simple one using a fixed size array of 256.

typedef std::basic_string< unsigned char > ustring;

class MessageProcessor
{
public:
virtual void processMessage( const ustring & msg ) = 0;
virtual ~MessageProcessor() {}
};

class MessageProcessorTable
{
private:
enum { tableSize=256 };

MessageProcessor* itsTable[ tableSize ];
public:
MessageProcessorTable()
{
std::fill_n( &itsTable[0], tableSize, 0 );
}

void addProcessor( unsigned char idx, MessageProcessor * pmp )
{
itsTable[ idx ] = pmp;
}
bool processMessage( const ustring & msg ) const
{
if ( !msg.empty() )
{
MessageProcessor * pmp = itsTable[ msg[0] ];
if ( pmp )
{
pmp->processMessage( msg );
return true;
}
}
return false;
}
};

Obviously you then create an instance of the table, instances of each
message and add them to the table, then process your messages as they
come in. And you can introduce error handling features where a message
could not be processed - log the error, throw an exception or however
you want to handle it.

And note this is an illustration.In reality you might separate the
definition and implementation of the classes into .h and .cpp files.

[Earl Purple]

Clark S. Cox III wrote:

On 2006-01-03 12:17:11 -0500, "Earl Purple" <ea********@gmail.com> said:
But then, you have to worry about managing the lifetime of the
pointed-to objects. If one were to simply store pointers to functions
in the container, then that issue goes away.

3 options:

1. Use smart pointers.
2. Use global objects. After all, these objects are only really
wrappers for functions so unless they hold state (thus potentially
being non-thread-safe to have global ones) it isn't really any
different. Certainly it can be no worse than using functions.
3. As I've put them (see my other post) into a table then the table can
delete them in its destructor. (Table would then also need overloaded
copy-constructor and assignment).

Most of the time I would go for option 2 in this situation. Often these
are actually objects that are dynamically loaded from a library. Note
that if you are programming using POSIX , this is the preferred way as
the result of dlsym is a void* pointer, i.e. a pointer to an object not
to a function.

(I might go for option 1 sometimes. Would rarely opt for 3 unless 2
wasn't an option and I needed higher performance than 1).