I wrote a custom container that represents a vector (I know I could just use std::vector, this is for education purposes). The class contains a pointer to some data and I’d really like to be able to see the data instead of just the value of the pointer when I’m debugging.

If I run the C++ code below using gdb and vscode and inspect the variable x, I get the following:

Even though I can’t see the contents of the vector, vscode recognizes that x is an object and I can collapse it to show less.

To show the data in the vector, I wrote a pretty printer (also listed below). If I use that, vscode shows the following:

The data is shown, but it is not being recognized as an object that can be collapsed it just shows the JSON string. Note that without the pretty-printer -exec print x in the debug console just outputs {size = 3, data = 0x55555556b2b0} so I thought it would be reasonable that JSON strings get formatted nicely.

What would it take to properly format these strings? Maybe a special formatting of my JSON? Maybe I just switch to lldb? Any help is appreciated.

// test_vector.cpp
#include <iostream>
#include <cassert>

class my_vector {

    public:
        my_vector(int n) : size(n), data(new double[n]) {}

        ~my_vector() {
            delete[] data;
        }

        double& operator[](int i) {
            assert(i >= 0 && i < size);
            return data[i];
        }

    private:
        int size;
        double* data;

};

int main()
{

    my_vector x(3);

    x[0] = 1;
    x[1] = 2;
    x[2] = 3;

    return 0;
}

// vector.py
class VectorPrinter:
    def __init__(self, val):
        self.val = val

    def to_string (self):
        n = self.val['size']
        data = self.val['data']

        out = "{"
        out += "size = " + str(n)

        out += ", data_ = {"
        for i in range(n-1):
            out += str(data[i]) + ", "
        out += str(data[n-1])
        out += "}"
        out += "}"

        return out

def lookup_type (val):
    lookup_tag = val.type.tag
    if lookup_tag is None:
        return None
    
    if( lookup_tag == "my_vector" ):
        return VectorPrinter(val)
    
    return None

gdb.pretty_printers.append (lookup_type)