« Double pointers

Simplify Double Pointers

Copy
1int i = 10;
2int *p = &i;
3int **dp = &p;
4
5//same values for below 2 lines
6cout << "&p: " << &p << endl;
7cout << "dp: " << dp << endl;
8
9
10//same values for below 2 lines
11cout << "p: " << p << endl;
12cout << "*dp: " << *dp << endl;
13
14
15//same values for below 3 lines
16cout << "i: " << i << endl;
17cout << "*p: " << *p << endl;
18cout << "**dp: " << **dp << endl;

Above means p is a pointer to a int and dp is a pointer to int* which is a pointer. So dp is a double pointer

Passing double pointers to functions

Copy
1void increment1(int **p)
2{
3    p = p + 1;
4}

Copy
1void increment2(int **p)
2{
3    *p = *p + 1;
4}

Copy
1void increment3(int **p)
2{
3    **p = **p + 1;
4}

Final code:

Copy
1#include <iostream>
2#include <iomanip>
3#include <algorithm>
4#include <string>
5#include <cstring>
6#include <vector>
7#include <cmath>
8#include <map>
9#include <climits>
10// climits for INT_MIN
11#include <unordered_map>
12using namespace std;
13
14void increment1(int **p)
15{
16    p = p + 1;
17}
18
19void increment2(int **p)
20{
21    *p = *p + 1;
22}
23
24void increment3(int **p)
25{
26    **p = **p + 1;
27}
28
29int main()
30{
31    int i = 10;
32    int *p = &i;
33    int **dp = &p;
34
35    cout << "&dp: " << &dp << endl;
36
37    // same values for below 2 lines
38    cout << "&p: " << &p << endl;
39    cout << "dp: " << dp << endl;
40
41    // same values for below 2 lines
42    cout << "p: " << p << endl;
43    cout << "*dp: " << *dp << endl;
44
45    // same values for below 3 lines
46    cout << "i: " << i << endl;
47    cout << "*p: " << *p << endl;
48    cout << "**dp: " << **dp << endl;
49
50    return 0;
51}