no matching function for call error C++

[pozdrav]

Hi,
I have a vector class vec. Now, I am creating custom utility functions using function templates. For example,

template <class T>
T sum(vec<T> &v) {
    // calculate th sum of vector and return the value
}

template <class T>
vec<T> & find(vec<T>& v, const int val) {
    // find all values where v[i] == val and return in vector
}

Here I have 2 questions.
1) when I try to call these functions in a chain fashion (last part of the code below),

// create sample vector
int a[5] = {1,2,5,4,5};
vec<int> v(a,5);

// code that works
vec<int> v_find = find(v, 5);
int s = sum(v_find);

// code that results in error 
// error: no matching function for call to ‘sum(vec<int>)’ 
// note: candidates are: T sum(vec<T>&) [with T = int]

int s = sum(find(v,5));

I see that the problem is because of the difference in the function definition, I obtain the address of input object in the functions and here, I pass by value. I don't want to change at the function implementation. In that case, how do you suggest I can implement this line directly without error?

2) How can I limit this sum function template to operate only on int, float, double data types alone (without writing 3 different functions of course)?

thank you.

[firedraco]

1) In your find() function, don't return a reference, you should be returning a copy. (I think)

2) Why? What if someone wants to sum a bunch of BigInts up? If they pass types that don't work, they will get a compile time error anyway.

[pozdrav]

1) I am sorry that was a typo. The function definition is,

template <class T>
vec<T> find(vec<T>& v, const int val) {
    // find all values where v[i] == val and return in vector
}

But still I get the error. I suppose its because the input argument to sum() is passed by reference? And I don't want to change this.

2) Well, apart from that fact that, it was just a matter of knowing, it could be used to limit from being used against char or if a specific function shouldn't operate on bool etc... Its done using #ifndef ?

thank you.

[chrisname]

1. I would assume the error is because you're dereferencing v, and v isn't a pointer.
2. Why would you make that restriction? There's no use in it -- I mean, theoretically I could do bool b = (bool)std::cin.get(); but I wouldn't because that would be stupid. The compiler would probably let me; but it would be detrimental to my program. Ultimately, I wouldn't want to do it. Compile errors are only there because the compiler doesn't know what to do with the code you gave it. The compiler generates a warning when you do something that could be detrimental to your program.

[jsmith]

The probably is that you cannot bind temporaries to non-const references. This is why, if using
references, you _must_ be const correct.

find returns a temporary. sum takes a non-const reference.

both sum and find should take const references.

[pozdrav]

Awesome! thank you very much. Yes, it solves the problem...
1 less problem... :) thanks again!