Question

I found this symbols in a function declaration several times, but i don't know what they mean, if it is something stupid I apologize for the question.

like this:

That is taking the parameter by reference. So in the first case you are

taking a pointer parameter by reference so whatever modification you do

to the value of the pointer is reflected outside the function. Second is

 the simlilar to first one with the only difference being that it is a

 double pointer. See this example:


    void pass_by_value(int* p)
    {
    	//Allocate memory for int and store the address in p
    	p = new int;
    }
    
    void pass_by_reference(int*& p)
    {
    	p = new int;
    }
    
    int main()
    {
    	int* p1 = NULL;
    	int* p2 = NULL;
    
    	pass_by_value(p1); //p1 will still be NULL after this call
    	pass_by_reference(p2); //p2 's value is changed to point to the newly allocate memory
    
        return 0;
    }

In actual code or a book? To me it just looks like notation for a general function. One which returns a single pointer, and the other a pointer to a pointer. — Mr. Shickadance, Apr 26 '11 at 11:48
like this: void raccogli_dati(double **& V, double **p, int N) { int ultimo = 3; V = new double * [N/2]; for(int i=0; i < N/2; i++) { V[i] = new double[N/2], std :: clog << "digita " << N/2 - i << " valori per la parte superiore della matrice V: "; for(int j=i; j < N/2; j++) std :: cin >> V[i][j], p[ultimo++][0] = (V[i][j] /= sqrt(p[i][0]*p[j][0])); } for(int i=1; i < N/2; i++) for(int j=0; j < i; j++) V[i][j] = V[j][i]; } — sdffadsf, Apr 26 '11 at 11:49
yes, but what is the importance of using it in a function declaration, what are the difference with * and **, also with this syntax you don't copy the "values" — sdffadsf, Apr 26 '11 at 11:51

score 15 · Accepted Answer

That is taking the parameter by reference. So in the first case you are taking a pointer parameter by reference so whatever modification you do to the value of the pointer is reflected outside the function. Second is the simlilar to first one with the only difference being that it is a double pointer. See this example:

That is taking the parameter by reference. So in the first case you are taking

 a pointer parameter by reference so whatever modification you do to the value

of the pointer is reflected outside the function. Second is the simlilar to

first one with the only difference being that it is a double pointer. See

this example:


    void pass_by_value(int* p)
    {
    	//Allocate memory for int and store the address in p
    	p = new int;
    }
    
    void pass_by_reference(int*& p)
    {
    	p = new int;
    }
    
    int main()
    {
    	int* p1 = NULL;
    	int* p2 = NULL;
    
    	pass_by_value(p1); //p1 will still be NULL after this call
    	pass_by_reference(p2); //p2 's value is changed to point to the newly allocate memory
    
        return 0;
    }

7 Answers