Is there any way to use parameters from the constructor in a c++ header Flie

Question

i want to use values that I declare in the constructor with passed variables in the Header file. Is that somehow possible? In my case I give the constructor two int values with these values I want to set the size of a array. Was there a way to do that in the header file? Like this:

class test
{
public:
    test(int valueA);  //Constructor
 float testArray [valueA];  //Array
}

Spell it `std::vector`, and you'll find it works beautifully — StoryTeller - Unslander Monica, Mar 17 '20 at 07:32
`ecgxChannel` is no constructor for `test`, that's probably a typo? — Lukas-T, Mar 17 '20 at 07:34
There's is no 2D array in your sample code. Do you mean a 1D array or a 2D array? The recommendation would be different in each case. — john, Mar 17 '20 at 07:36

score 3 · Answer 1 · answered Mar 17 '20 at 07:36

3

No you can't do it like this and no, that's not even legal C++. The size of an array must be known at compile time. You should use std::vector<float> instead and initialize it in the constructors initializer list:

#include <vector>

class test
{
public:
    test(int valueA) : testArray(valueA) {}
    std::vector<float> testArray; 
}

This will initialize testArray with valueA values.

answered Mar 17 '20 at 07:36

Lukas-T

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is that also possible for 2-D Vectors? – MB1995 Mar 17 '20 at 13:08
@MB1995 Yes, there are many question that cover this topic. [This one](https://stackoverflow.com/questions/17663186/initializing-a-two-dimensional-stdvector) for example. – Lukas-T Mar 17 '20 at 14:09

John3136 · Answer 2 · 2020-03-17T07:44:16.450

As written: no.

Two options:

Use a class that doesn't need it's size set (like std::vector). This is the better approach.

Or dynamically create the array once you do know the size. This isn't a great approach, but may be closer to the intent of the original question. As pointed out in the comments to avoid dynamic memory issues, since there is a destructor you probably want a copy constructor and a copy assignment constructor to ensure you don't end up with two text classes sharing the same array.

class test
{
public:
    test(int valA)
    {
        testArray = new float[valA];
    }

    ~test()
    {
        delete[] testArray;
    }
private:
    float* testArray
};

Is there any way to use parameters from the constructor in a c++ header Flie

2 Answers2