Two different outputs from functions

Question

#include <iostream>
#include <iomanip>
#include <ctime>

using namespace std;

char* InitializingMatrix(char start, char end) {
    char matrix[9];

    //Initializing random symbols to char massive
    srand((unsigned)time(0));
    for (int i = 0; i < 9; i++)
        matrix[i] = (int)start + rand() % (int)end;

    //Output matrix
    for (int i = 0; i < 9; i++)
        (i == 3 || i == 6) ? cout << endl << (char)matrix[i] << " " : cout << (char)matrix[i] << " ";
    cout << endl;

    return matrix;
}

void Output(char matrix[]) {
    //Output matrix
    for (int i = 0; i < 9; i++)
        (i == 3 || i == 6) ? cout << endl << (char)matrix[i] << " " : cout << (char)matrix[i] << " ";
}


int main() {
    Output(InitializingMatrix('1', '6'));
    return 0;
}

Problem

The output of the matrix from the function for initializing the matrix and from the function for outputting the matrix are different.

Questions

Why output from InitializingMatrix and Output have differences?

How to fix it?

[What is a debugger and how can it help me diagnose problems?](https://stackoverflow.com/questions/25385173/what-is-a-debugger-and-how-can-it-help-me-diagnose-problems) — Jason, Oct 23 '22 at 12:42
[Why is "using namespace std;" considered bad practice?](https://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice) — Jesper Juhl, Oct 23 '22 at 12:53
[Warnings](https://stackoverflow.com/questions/57842756/why-should-i-always-enable-compiler-warnings) are your friends. [Enable them](https://godbolt.org/z/8M98Kc1Yz). — n. m. could be an AI, Oct 23 '22 at 13:00

score 1 · Accepted Answer · answered Oct 23 '22 at 12:56

The issue that you return a Pointer but you allocate a Value.

Allocation:

char matrix[9];

Return value:

char* InitializingMatrix(...)

Type char matrix[] is a compiled time array.
If you wish to use arrays you'll need to use new char() instead to dynamically allocate a new array.

The C++ OOP way is to use a class:

Use the built in type std::array<...>
Create a class and save the array in there:

struct MyData 
{
  char Data[10];
}

The compiler would help you pass this around by value or use a ref to pass it by reference instead:

MyData Initialize() { ... };

void Output(MyData& data);
//or
void Output(const MyData& data);

int main() 
{
    MyData data = Initialize();
    Output(data );
    return 0;
}

The more professional way is to use built-in types or frameworks that exist, If you need a matrix you can use libraries like GMTL or EIGEN

@NeilButterworth Refrain from making such comments without explaining yourself. — SimplyCode, Oct 23 '22 at 20:46

Two different outputs from functions

1 Answers1