looser exception specification on overriding virtual function

Question

I have a template Matrix class:

template <typename T, int row, int col>
class Matrix{};

Inside the class decleration I wrote an execption class, based on std::exception:

class MatrixException: public std::exception
{
private:
    const char* errmsg;
public:
    MatrixException(const char* msg="")
        :errmsg(msg) {} 
    const char* what() const {return errmsg;}
};

class IllegalOperation: public MatrixException
{
    public:
        IllegalOperation(const char* msg="")
            : MatrixException(msg) {}
};

I tried to use it on one of the class' functions, int the implantation part, like this:

template <typename T, int row, int col>
Matrix<T, row, col>& Matrix<T, row, col>::operator=(const Matrix& mat)
{
    if (condition)
        {throw IllegalOperation("Matrices sizes don't match");}
    // other stuff
    return *this;
}

and I get this error message: looser exception specification on overriding virtual function 'const char* Matrix<T, row, col>::MatrixException::what() const [with T = int; int row = 3; int col = 3]'|

What did I do wrong?

ADDITION: I've tried one of the linked below, and it helped me. Though I did try to find a similar question myself. I've changed the line

const char* what() const {return errmsg;} to

const char *what() const noexcept {return errmsg;} and it was ok. Thanks whoever put the links!

[`what()`](https://en.cppreference.com/w/cpp/error/exception/what) should be also marked `noexcept`. — Yksisarvinen, Apr 26 '23 at 16:45
Because if your exception handler throws unexpectedly, what then? — Paul Sanders, Apr 29 '23 at 11:00
@PaulSanders I have a try-catch in my main. It's a part of hw assignment, the function SHOULD fail and write a message on the screen. — Superot, Apr 29 '23 at 11:07
OK, but if it's calling `what()`, and `what()` throws, then you'll never see that message. That's why `what()` needs to be `noexcept` (and shouldn't throw!). — Paul Sanders, Apr 29 '23 at 11:39

looser exception specification on overriding virtual function

0 Answers0