How to format output like this - c++

Question

My code is like this so far :
void matrix::print(int colWidth) const
{
cout << getRows() << " x " << getCols() << endl;
cout << "-";
for (unsigned int d = 0; d < getCols(); d++) {
cout << "--------";
}
cout << endl;
for (unsigned x = 0; x < getRows(); x++) {
cout << "|";
for (unsigned y = 0; y < getCols(); y++) {
cout << setw(colWidth) << at(x, y) << " |";
}
cout << endl;
}
cout << "-";
for (unsigned int d = 0; d < getCols(); d++) {
cout << "--------";
}
cout << endl;
}
But the output depends on the colWidth which will be the space between each number printed. So how can I adjust my dashes to be printed like the following no matter the colWidth it should align.
One output should look like this:
Second output is like this:

Answer 1

If the column width is a parameter, you're almost done with your code. Just turn the cout<<"--------" into:
std::cout << std::string(getCols()*(colWidth + 2) + 1, '-');
That code prints a string of dashes, which width is: number of matrix columns, times column width plus 2, plus 1:
Plus 2 because you are appending a " |" to each column.
Plus 1 because you are adding a '|' at the beginning of each row.
You may want to check for empty matrices at the beginning of your print method.
[Demo]
#include <initializer_list>
#include <iomanip> // setw
#include <iostream> // cout
#include <vector>
class matrix
{
public:
matrix(std::initializer_list<std::vector<int>> l) : v{l} {}
size_t getRows() const { return v.size(); }
size_t getCols() const { if (v.size()) { return v[0].size(); } return 0; }
int at(size_t x, size_t y) const { return v.at(x).at(y); }
void print(int colWidth) const
{
std::cout << "Matrix: " << getRows() << " x " << getCols() << "\n";
// +2 due to " |", +1 due to initial '|'
std::cout << std::string(getCols()*(colWidth + 2) + 1, '-') << "\n";
for (unsigned x = 0; x < getRows(); x++) {
std::cout << "|";
for (unsigned y = 0; y < getCols(); y++) {
std::cout << std::setw(colWidth) << at(x, y) << " |";
}
std::cout << "\n";
}
std::cout << std::string(getCols()*(colWidth + 2) + 1, '-') << "\n";
}
private:
std::vector<std::vector<int>> v{};
};
int main()
{
matrix m{{1, 2}, {-8'000, 100'000}, {400, 500}};
m.print(10);
}
// Outputs
//
// Matrix: 3 x 2
// -------------------------
// | 1 | 2 |
// | -8000 | 100000 |
// | 400 | 500 |
// -------------------------