C++ 2 Dimensional Dynamical Array with Pointer String

Question

I see a lot of video and explanation about 2 dimensional array with double pointer which is possible when you are storing int, but what if I wanna store string in that 2 dimensional dynamical array?

For example, I'm planning to input my files into my 2 dimensional dynamical array which depends on how many accounts or data I have in my files.

Let's say I have 2 now, and in my program I add 1 more account, which is going to be 3, let say each of my arrays only has 3 elements inside, and then besides that, I do not want to set a constant array.

How am I going to set a variable of two dimensional dynamical array that stores the string? like the very simple one.

Edit : And can also someone explain me why do we have to delete after using the dynamical array? like what if I store something? does it mean my elements also get deleted? or when we close the console it will distract the actual memory? I do not really understand.

Why not simply std::vector<std::string>? You then append as many strings as you want to without having to care for memory management... Technically it is equivalent to a jagged 2d array using raw pointers. — Aconcagua
– Aconcagua, Commented Sep 6, 2021 at 12:05
@Ruks here you go, int** array = new int*[rows]; and then for (int i = 0; i < rows; i++){int[i] = new int[cols]}; — Meilianto Luffenz
– Meilianto Luffenz, Commented Sep 6, 2021 at 12:19

Botond Horváth · Accepted Answer · 2021-09-06 12:24:28Z

3

string** array = new string*[rows];
for (int i = 0; i < rows; i++)array[i] = new string[cols];}

or

vector<vector<string>> array;

answered Sep 6, 2021 at 12:24

Botond Horváth

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1 Comment

Meilianto Luffenz Over a year ago

No way, I remember that I went through this trying to use string, but It couldn't work. and I tried again after saw your comments, somehow it worked. thanks :)

sehe · Accepted Answer · 2021-09-06 12:24:55Z

1

In C++, in principle don't do manual memory management.

You can use vectors for dynamic arrays. Here's a sample that also shows how to grow both dimensions:

Live On Compiler Explorer

#include <string>
#include <vector>
#include <fmt/ranges.h>

int main() {
    std::vector<std::vector<std::string> > arr 
    {
        { "account 1", "foo", "bar" },
        { "account 2", "qux", "quz" },
    };

    fmt::print("Before: {}\n", fmt::join(arr, "\n\t"));

    // add a row
    arr.push_back({"account 3", "yo", "lo"});
    fmt::print("Extra row: {}\n", fmt::join(arr, "\n\t"));

    // add a column
    for (auto& row : arr)
        row.push_back("extra");
    fmt::print("Extra column: {}\n", fmt::join(arr, "\n\t"));
}

Prints

Before: {"account 1", "foo", "bar"}
        {"account 2", "qux", "quz"}
Extra row: {"account 1", "foo", "bar"}
        {"account 2", "qux", "quz"}
        {"account 3", "yo", "lo"}
Extra column: {"account 1", "foo", "bar", "extra"}
        {"account 2", "qux", "quz", "extra"}
        {"account 3", "yo", "lo", "extra"}

answered Sep 6, 2021 at 12:24

sehe

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2 Comments

sehe Over a year ago

Add demo Live On Compiler Explorer

Meilianto Luffenz Over a year ago

Thanks, it really helpful.

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