Parameters and functions in C++

Question

Let's suppose this code:

void function(const float vect[]){

// making something with "vect" here (not modifying as it is const)

};

then in the main function:

float v[5];

function(v+2);

Is it correct to call the function like that? What exactly I'm passing to that function doing that?

Answer 1

The array will decay to pointer during the call

so you're basically doing this :-

+---+---+---+---+---+
|   |   |   |   |   |
+---+---+---+---+---+
 ^    ^   ^   ^   ^
 |    |   |   |   |
 v   v+1 v+2 v+3 v+4
          ^
          |
function(v+2); //In "function" v will be used from v+2, i.e. vect[0] will be v[2]

Answer 2

To understand this you have to understand that sometimes C++ lies.

void function(const float vect[]){ is not a function taking an array as a parameter (that's the lie). Instead it's exactly the same as if you had written this void function(const float* vect){ . Now it's easier to understand, your function takes a pointer, so when you write function(v+2); you are passing a pointer to the third element of your array, just as when you write function(v); you are passing a pointer to the first element of your array.

It's impossible to pass an array to a function in C++ (or return an array from a function), arrays are always converted into pointers in these situations.

Answer 3

Is it correct to call the function like that?

As long as you don't access the array out of bounds (ie you only read vect[0] , vect[1] or vect[2] ), it is.

What exactly I'm passing to that function doing that?

I don't understand this question. If you want to know what this does: the v array decays into a pointer, then the + operator performs pointer arithmetic on it, and a pointer to of the third element (ie the one at index 2) is passed to the function.