What's the best way to fill multiDimensional Array

Question

I am trying to find the best way to fill 2D Array with a specific value. Is there any better way to loop the 2D Array? I tried memset doesn't work I tried std::fill but I doubt there is something wrong with my code.

void fillMultipleArray(int m, int n, int value)
{
    int grid[m][n];
    
    memset(grid, 0, sizeof(grid));
    
    
    for (int i = 0; i < m; i++) {
        
        for (int i = 0; i < n; i++) {
            
            std::cout << grid[m][n] << std::endl;
        }
    }    
}

Output

-272632896 -272632896 -272632896 -272632896 -272632896 -272632896 -272632896 -272632896

Thanks in advance

@M.A haven't tested, but are you sure that doesn't just set the first one as 666 and the rest of the elements as 0? — mediocrevegetable1, Feb 17 '21 at 08:44
Don't fix the code in your question, it invalidates the posted answer. — Blastfurnace, Feb 17 '21 at 08:53
BTW, `int grid[m][n];` is a [non-standard VLA](https://stackoverflow.com/questions/1887097/why-arent-variable-length-arrays-part-of-the-c-standard). — Bob__, Feb 17 '21 at 09:03

score 1 · Answer 1 · answered Feb 17 '21 at 08:40

1

Using memset is fine, instead look carefully at your printing code, it has multiple mistakes

for (int i = 0; i< m; i++) {
    for (int i = 0; i< n; i++) {
        std::cout<< grid[m][n]<< std::endl;
    }
}

That should be

for (int i = 0; i < m; i++) {
    for (int j = 0; j < n; j++) {
        std::cout<< grid[i][j] << std::endl;
    }
}

It's a good lesson, when the output is wrong, it could be because your calculation is wrong, but it could just as easily be that you are printing your results wrong. Try not to make too many assumptions.

answered Feb 17 '21 at 08:40

john

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for (int j = 0; j < n; i++) should be j++ – ΦXocę 웃 Пepeúpa ツ Feb 17 '21 at 08:44
1

@ΦXocę웃Пepeúpaツ Yes I've fixed it – john Feb 17 '21 at 08:44
Yea I fixed the code printing but it's still giving the same error also i tried this memset but still having the same problem memset(grid, 0, sizeof(int) *m*n); – ymyh Feb 17 '21 at 08:45
Yea it works if tried memset(grid, 0, sizeof(int) *m*n); – ymyh Feb 17 '21 at 08:46
Thanks alot the code has been updated to the working one – ymyh Feb 17 '21 at 08:47
1

@youssefmyh Do you realise that `int grid[m][n] ;` is not legal C++? In C++ array sizes must be constants, but `m` and `n` are variables. – john Feb 17 '21 at 08:47
@john I am using the c++17 Xcode Mac and I am getting no warning. – ymyh Feb 17 '21 at 08:51
@youssefmyh That's because your compiler accepts invalid C++. See here https://stackoverflow.com/questions/39334435/variable-length-array-vla-in-c-compilers – john Feb 17 '21 at 08:53
@youssefmyh Presumably this is why `sizeof(grid)` didn't work. That would work with a legal C++ array. – john Feb 17 '21 at 08:55

What's the best way to fill multiDimensional Array

1 Answers1