C++ pass an array by reference

As you are using C++, the obligatory suggestion that's still missing here, is to use std::vector<double>.

You can easily pass it by reference:

void foo(std::vector<double>& bar) {}

And if you have C++11 support, also have a look at std::array.

For reference:

• http://de.cppreference.com/w/cpp/container/vector
• http://de.cppreference.com/w/cpp/container/array

Yes, but when argument matching for a reference, the implicit array to pointer isn't automatic, so you need something like:

void foo( double (&array)[42] );

or

void foo( double (&array)[] );

Be aware, however, that when matching, double [42] and double [] are distinct types. If you have an array of an unknown dimension, it will match the second, but not the first, and if you have an array with 42 elements, it will match the first but not the second. (The latter is, IMHO, very counter-intuitive.)

In the second case, you'll also have to pass the dimension, since there's no way to recover it once you're inside the function.

Arrays can only be passed by reference, actually:

void foo(double (&bar)[10])
{
}

This prevents you from doing things like:

double arr[20];
foo(arr); // won't compile

To be able to pass an arbitrary size array to foo, make it a template and capture the size of the array at compile time:

template<typename T, size_t N>
void foo(T (&bar)[N])
{
    // use N here
}

You should seriously consider using std::vector, or if you have a compiler that supports c++11, std::array.