Display a particular std::vector's element in GDB pretty printer

Question

Suppose I have a simple struct:

struct S {
    int index;        
    const std::vector<int>& vec;
};

I want to write a pretty printer for GDB that would display vec[index] for an object of type S.

This is how I do it now:

class SPrinter:
    def __init__(self, name, val):
        self.val = val

    def to_string(self):
        i = int(self.val['index'])
        ptr = self.val['vec']['_M_impl']['_M_start'] + i
        return str(ptr.dereference())

Is there a simpler way to access the given element of std::vector? Is it possible to call operator[] (in GDB I can do p s.vec[0] and get what I want)? I'd like my printer to be independent of the particular implementation of std::vector.

Evg · Accepted Answer · 2018-12-22T11:18:42.383

After reading this answer, I came up with the following solution:

def get_vector_element(vec, index):
    type = gdb.types.get_basic_type(vec.type)
    return gdb.parse_and_eval('(*(%s*)(%s))[%d]' % (type, vec.address, index))

class SPrinter(object):
    def __init__(self, name, val):
        self.val = val

    def to_string(self):
        return get_vector_element(self.val['vec'], int(self.val['index']))

Display a particular std::vector's element in GDB pretty printer

1 Answers1