c++debuggingvisual-studio-2019stdvectordebuggervisualizer

In Visual Studio 2019 C++, how can I expand a dynamically allocated array so that all of its elements are displayed?


I've written a simple (and potentially bad) implementation for a vector class, similar to std::vector.

Here is the class:

template <class T>
class Vector
{
    T* data;
    int size;
public:
    Vector(int = 0);
    ~Vector();

    Vector(const Vector<T>&);
    
    Vector<T>& operator=(Vector<T>);
    T& operator[](int);

    friend void swap(Vector<T>&, Vector<T>&);

    void Clear();
    void Insert(T, int);
    void Delete(int);
    int Size();
};

When debugging code that uses my vector, I've noticed that the pointer that I'm using internally only expands up to the first element normally.

I found this SO question, How to display a dynamically allocated array in the Visual Studio debugger?, which seems to give a simple solution to the problem, but I'm wondering if it's possible to expand the array by a non-constant amount (say, the current vector size).

Considering that std::vector does show all of its elements normally inside the debugger, could I alternatively rewrite my vector to include that functionality?

Here is a snip of the "Locals" tab with some test variables, to show what I'm referring to:


Solution

  • It seems that I found how to do this using .natvis files.

    This article provides more details about Natvis files: https://learn.microsoft.com/en-us/visualstudio/debugger/create-custom-views-of-native-objects?view=vs-2019

    Adding a .natvis file to your project allows you to specify how the container should be displayed in Locals.

    Here is a simple example for the Vector container described in the original post:

    <?xml version="1.0" encoding="utf-8"?> 
    <AutoVisualizer xmlns="http://schemas.microsoft.com/vstudio/debugger/natvis/2010">
      <Type Name="AC::Vector&lt;*&gt;">
        <DisplayString>{{ size={size} }}</DisplayString>
        <Expand>
          <Item Name="[size]" ExcludeView="simple">size</Item>
          <ArrayItems>
            <Size>size</Size>
            <ValuePointer>data</ValuePointer>
          </ArrayItems>
        </Expand>
      </Type>
    
    </AutoVisualizer>
    

    After creating the file and starting the debug session, the container now displays its contents properly:

    AC::Vector<int> myVec(3);
    myVec[0] = 1;
    myVec[1] = 2;
    myVec[2] = 3;
    

    Locals:

    enter image description here