C++ Pointers

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Array of pointers to ints

Code:

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#include <iostream>

int main()
{
    int* ap[15];
    int ai[15] = {};
    for (int i = 0; i < 15; ++i) {
        ai[i] = i; 
        ap[i] = &ai[i];
        std::cout << *ap[i] << " " << ap[i]<< std::endl;
    }
}

Console:

0 0x16d296d14
1 0x16d296d18
2 0x16d296d1c
3 0x16d296d20
4 0x16d296d24
5 0x16d296d28
6 0x16d296d2c
7 0x16d296d30
8 0x16d296d34
9 0x16d296d38
10 0x16d296d3c
11 0x16d296d40
12 0x16d296d44
13 0x16d296d48
14 0x16d296d4c

Pointer to an array of ints

Code:

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#include <iostream>

int main()
{
    int ai[15];
    for (int i = 0; i < 15; i++) ai[i] = i;
    int (*ptr)[] = &ai;
    for (int i = 0; i < 15; i++) {
        std::cout << (*ptr)[i] << " ";
    }
}

Console

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Notes

  • The parentheses around *ptr are necessary because the [] operator has
    higher precedence than the * operator. Without the parentheses, the
    declaration would be parsed as an array of pointers to int, like int
    *ptr[15].

  • When I took the address of the array, I got a pointer to the first element
    of the array. However, the pointer itself does not contain any information
    about the size of the array.

Pointer to function taking a string argument;

returns an string

Code:

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#include <iostream>
#include <string>

void replaceX(std::string *str, std::string x)
{
    size_t pos = (*str).find("${x}");
    if (pos != std::string::npos)
        (*str).replace(pos, 4, x);
}

std::string foo(std::string x)
{
    std::string str = "hello this is ${x}";
    replaceX(&str, x);
    return str;
}

int main()
{
    std::string (*fp)(std::string) = &foo;
    std::cout << (*fp)("foo") << std::endl;
    std::cout << (*fp)("bar") << std::endl;
}

Console:

hello this is foo
hello this is bar