Template functions in C++ for immutable arrays - c++

Question

I'm trying to create a template function that will return true if a value from an immutable array exists, and false otherwise. Here is the code:
#include <algorithm>
using std::find;
#include <vector>
using std::vector;
template<class T>
bool contains(const T *arr, int size, T val) {
vector<T> dest(arr, arr + size);
T *p = find(dest.begin(), dest.end(), val);
if (p == arr + size)
return false;
else
return true;
}
Every time I compile against a simple test program I get these errors:
main.cpp:10: instantiated from 'void testit(const T*, int, T) [with T = char]'
main.cpp:37: instantiated from here
main.cpp:69: error: cannot convert '__gnu_cxx::__normal_iterator<char*, std::vector<char, std::allocator<char> > >' to 'char*' in initialization
main.cpp: In function 'bool contains(const T*, int, T) [with T = int]':
main.cpp:10: instantiated from 'void testit(const T*, int, T) [with T = int]'
main.cpp:43: instantiated from here
main.cpp:69: error: cannot convert '__gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> > >' to 'int*' in initialization
main.cpp: In function 'bool contains(const T*, int, T) [with T = std::string]':
main.cpp:10: instantiated from 'void testit(const T*, int, T) [with T = std::string]'
main.cpp:44: instantiated from here
(All of those errors are on the line that contains the find function)
What is the best way to go about this? Is the vector even neccessary?

Answer 1

Is the vector even neccessary?
No.
template<class T>
bool contains(const T *arr, int size, T val) {
return std::find(arr, arr + size, val) != arr + size;
}

Answer 2

If the argument is not an actual, complete array T.C.'s answer's solid (though taking the value by reference is a good idea), but if you only want to support entire arrays you can have something a smidge easier to use, with the array size extracted from the array's type:
template <class T, size_t N>
inline bool contains(const T(&arr)[N], const T& val)
{
return std::find(arr, arr + N, val) != arr + N;
}
Of course you can have both versions overloaded.

Answer 3

error: cannot convert '__gnu_cxx::__normal_iterator > >' to 'char*' in initialization
This is telling you the return type you have is not correct for std::find.
For the code you have, you should have something like the following.
template<class T>
bool contains(const T *arr, int size, T val)
{
vector<T> dest(arr, arr + size);
vector<T>::iterator p = find(dest.begin(), dest.end(), val);
return p != dest.end();
}
Is the vector even neccessary?
No, it could be simplified as follows.
template<class T>
bool contains(const T *arr, int size, T val)
{
const T* end = arr + size;
return find(arr, end, val) != end;
}