访问2D结构时程序崩溃

Question

So I have spent countless hours trying to find the answer to this question. I have found something close to it but not exactly so I guess I will post here.

I'm trying to create a 2D array of structs. I will call a function to create the struct and input values into the struct. This is an example of a possible output:

input: int 5, int 5

1 2 3 4 5
2 4 6 8 10
3 6 9 12 15
4 8 12 16 20
5 10 15 20 25

I was able to create the struct but my program keeps crashing when I try to input the values. Any inputs would be great! Here's my code below.

struct values{
int mult;
float div;
};

values** create_table(int row, int col){
values** tab = new values*[row];
values* one_row = new values[col];
for (int i = 0; i < row; i++){
    tab[i] = one_row;
}
return tab;
}

void set_m_values(values** tab, int row, int col){
for (int i = 0; i < row; i++){
    for (int j = 0; i < col; j++){
        tab[i][j].mult = (i+1)*(j+1);
    }
}
}

int main() {
int row = 5;
int col = 5;
values** tab = create_table(row, col);
set_m_values(tab, row, col);
for (int i = 0; i < row; i++){
    for (int j = 0; j< col; j++){
        cout <<tab[0][i].mult;
    }
    cout <<endl;
}
return 0;
}

Answer 1

Your initialization is wrong

values* one_row = new values[col];
for (int i = 0; i < row; i++){
    tab[i] = one_row;

This is creating one row, and assigning it to every row.

You probably meant to do:

values** tab = new values*[row];

for (int i = 0; i < row; i++)
{
    tab[i] = new values[col];
}

That being said you really should be using either std::array or std::vector .

ALSO, and this is what's causing the crash, in set_m_values , you have an incorrect comparison:

for (int j = 0; i < col; j++){ // notice the i in there

should be:

for (int j = 0; j < col; j++){ // replaced i with j

Most likely you copy pasted and forgot to change it. I would like to stress the fact that you really should be using standard library containers like vector for this. For example you could have:

// with this you don't need the create_table function
std::vector< std::vector<values> > table(row, std::vector<values>(col));

PS: You have a memory leak in your code because deletes are not called. Which is not a problem you would have with std::vector