Vector containing function of a class

Question

I am currently trying to create a vector containing function of a class .

Here is my code :

typedef leap::float64 (DataReader::*getFonction)();

std::vector<getFonction> vec;
std::vector<getFonction>::iterator it;

vec.push_back(&DataReader::getLa);
vec.push_back(&DataReader::getLon);

for(it = vec.begin(); it<vec.end(); it++)
    std::cout << *it << std::endl;

The function "get ..." (not static ) returned values are stored on shared resources and already initialized. But then , they return me only the values '1'.

An idea?

What do you expect to be output when you try to print a function pointer? It is implicitly being converted to `bool`. — TartanLlama, Aug 13 '15 at 13:41
You need an instance to call member function pointer using `.*` or `->*` — Jarod42, Aug 13 '15 at 13:43
You need to call the function. dereferencing the iterator is just going to give you a pointer value — NathanOliver, Aug 13 '15 at 13:43
And to second @NathanOliver: For calling the function you'll need to have a valid `DataReader` instance. — πάντα ῥεῖ, Aug 13 '15 at 13:44
Should we crosslink this question with [that one](http://stackoverflow.com/q/31988571/3233393) or something ? — Quentin, Aug 13 '15 at 13:57
@Quentin I knew I've seen it before today. The `getFonction` is very suspect. Hopefully the OP isn't using a sock puppet to probe their questions acceptance. — πάντα ῥεῖ, Aug 13 '15 at 14:28
@πάνταῥεῖ it's a follow-up question that other-side OP mistakenly posted as [an answer](http://stackoverflow.com/a/31988957/3233393). No clue what's going on. — Quentin, Aug 13 '15 at 14:30

TartanLlama · Accepted Answer · 2015-08-13T13:55:45.950

When you dereference it and output it, you are just printing out a representation of the function pointer, which is being implicitly converted to bool and output as 1 because it is not null.

If you want to call the function and output the return value, you need to call it on an instance:

DataReader reader;

for(it = vec.begin(); it<vec.end(); it++)
    //dereference it to get member function pointer and call it on reader
    std::cout << (reader.*(*it))() << std::endl;

If you are using C++11, std::function may be better suited:

using getFunction = std::function<leap::float64(DataReader&)>;

std::vector<getFunction> vec;
std::vector<getFunction>::iterator it;

vec.emplace_back(&DataReader::getLa);
vec.emplace_back(&DataReader::getLon);

DataReader reader;
for(it = vec.begin(); it<vec.end(); it++)
    std::cout << (*it)(reader) << std::endl;

Vector containing function of a class

1 Answers1