How do you implement a template function that accepts vectors and arrays

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I am attempting to assign random numbers to some array or vector
When I use this method on an array it works fine, however when I use this with an vector, it will not work.

C++

// declare small vector
vector <int> smallVector(smallSize);
// call helper function to put random data in small vector
genRand(&smallVector, smallSize);

I get this error:

C++

Error	3	error C2679: binary '=' : no operator found which takes a right-hand operand of type 'int' (or there is no acceptable conversion)

code:

C++

// function template for generating random numbers
template<class T> void genRand(T data, int size)
{
    for (int i = 0; i < size; i++)
    {
        data[i] = (1 + rand() % size);
    }
}

Posted 18-Oct-14 9:45am

joedoeuse

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2 solutions

Solution 1

Try leaving away the address-of operator while instantiating the function and pass the data in the template by reference.
Cheers
Andi

Posted 18-Oct-14 11:12am

Andreas Gieriet

Updated 18-Oct-14 11:13am

v2

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CubbiMew · Accepted Answer · 2014-10-18T11:14:00

Since data is an out-parameter (you're trying to populate it within genRand and make the result available in the caller, right?), you need to take it by reference:

C++

template<typename T>
void genRand(T& data, int size)
{   
 ...


genRand(smallVector, smallSize);
genRand(smallArray, smallSize);

(although you don't actually need to pass size in this case anymore: http://coliru.stacked-crooked.com/a/b47b6b14ca97ea8d[^])

Alternatively, you could use classic C++98 iterator interface:

C++

template<typename Iter>
void genRand(Iter beg, Iter end, int size)
{   
 ... // likely std::generate(beg, end, function);


genRand(smallVector.begin(), smallVector.end(), smallSize);
genRand(smallArray, smallArray + smallSize, smallSize);

(that also makes size an unnecessary parameter, it is simply end - beg)

What happened in your case was that you passed a pointer to the vector, so T was deduced to a pointer to a vector, data[i] evaluated to a vector, and since vector has no operator= that takes an int, you saw the error message.