How to pass solver workspace-size

I have an line detection Algorithm that uses a Solver(optimization Algo) to find some solutions for the line-detection problem.

class line-detect {
    public:
    (some functions);
    private:
    solver mSolve;
}

class Solver {
    public:
    (Some functions);
    private:
    (some functions);
}

In solver.cpp, the size of workspace/buffer used for solver computations is allocated using line-detect algo variables.

In Solver.cpp, size of workspace is allocated as below:

const uint32_t SIZEOF_WORKSPACE = static_cast<uint32_t>(((2 * NUM_ERRS_MAX) + (5 * NUM_VARS_MAX) + NUM_VARS_MAX * NUM_ERRS_MAX ) * sizeof(float64_t) + (NUM_VARS_MAX * sizeof(int32_t)));

Currently the solver is within the algo itself, but I want to extract out the solver and use as a separate entity/module. I have extracted the solver but this size workspace/buffer has to allocated statically(i.e I have to hard-coded the line-detect algo values in solver module)

Ques: What is the best possible way to allocate the size of workspace without having to hard-code the line-detect algo variables in the solver module ?