Return A Dynamically Allocated 2D Array From A Function | C Programming Tutorial

[battlelance]

Exactly the help I needed. Explained very clearly. Thank you

[MarcoAurelio-svtk]

I had a very hard time to understand this concept when trying to change the *stack values when doing a DFS. I learned that, even if we have a *stack, we need to set the parameter of the function to change the *stack to **stack like:

void change_stack(stack_t **stack, int value) // This is a pointer to the stack pointer and is needed to change/access the stack itself by dereferencing it later.

void stack_pop(stack_t **stack) {
if(!*stack) {
printf("Stack is empty\n");
return;
}

stack_t *old = *stack;

*stack = (*stack)->next;
free(old);
}

Otherwise, if the function is void change_stack(stack *stack, int value), it does not change the actual value. We need the pointer to *stack.

I learned this the hard way ahah

Thank you for your videos. You're being a monumental help

[Gabriel-wqlw]

This is the best so far, i`ve found about arrays in functions, even better than college ones.

[udarue]

this video should get more likes and views! Nice explanation!🙏

[virivirus]

Thank you so much. I was confused on how to return an array (didn't know you could use pointers like this).

[mins]

Is it possible to write code that produces the same result using the `static` keyword?

[NachoDev]

Thank you so much for this detailed explanation. I've been having trouble trying to understand the logic ✌️💪🙂

[andredcavalcante]

Another way is to create a single pointer, alocate all elements once and use some arithmetic to get correct a(i, j) element. In the end, free all elements once.

[eruhinmakhtar]

I would not advise allocating a 2D array like this because the multiple malloc calls fragment the array across memory, which has significant impacts on performance. Instead you should allocate one big array of [m*n] and then typecast the array to [m][n]

[TL-fesi]

If I understand the subject correctly, this is not exactly a 2d array in C. The returned matrix functions as if it's a 2d array, but in fact, it is a 1d array of pointers, each pointer points to the first element of a 1d array. This is different compared to an actual 2d array created by the following code:
int a[2][3]; // where a will decay to a pointer to a whole 1d array of size 3, i.e., int (*ptr)[3];

[nathanassefa]

this is really helpful. Thank you so much!

[qwertyqwerty]

It's better to store matrix in an 1D array by rows or by columns (in fortran manner). See LAPACK interface, for instance.

[AnalogDude_]

Weird, when an 100% identical "solution" as written in the main function, i mean code syntax, cannot be applied in a function below main. (*arrayPTR)[i] vs *(int*)arrayPTR + i).

[abdullah.sherdy]

why use malloc(sizeof(int*)*m) to allocate space for rows in 2d array ?

[karimshariff]

I understand from a "monkey see monkey do" point of view. However, I don't see how the syntax jives with what is happening under the hood. (1) To access any element A[i][k], the compiler just needs a pointer to the first element and the size of the array. Why does it need a pointer to a pointer. (2) Also, is it true that all that the compiler keeps track of is a single pointer for the first element of the array, rather than "m" pointers for each row of the array? Thanks.

[juanmacias]

Awesome vid, I tried making a snake game, but stuck on a seg fault lol taking a break for now.