gdb: show typeinfo of some data

Question

Basically, I want to get typeid(*this).name(), i.e. the real type of this.

I want to get this in GDB (without modifying the source code). I

Answer 1

This question may be related: vtable in polymorphic class of C++ using gdb:

(gdb) help set print object
Set printing of object's derived type based on vtable info. 

It's not exactly typeid() but it should show the real object type when inspecting a polymorphic pointer (e.g. this in a base class). Naturally works only for classes with a vtable (i.e. at least one virtual method) but so does typeid.

Answer 2

Use ptype command, like this:

(gdb) ptype 42
type = int

Answer 3

The 'ptype [ARG]' command will print the type.

Answer 4

As @Star Brilliant says here, this:

ptype my_var

returns things like type = unsigned short, but I want it to return type = uint16_t instead, so I can truly know how many bytes it is when inspecting memory. The best I can figure out to get this effect is to do:

print &my_var

which prints (uint16_t *) 0x7ffffffefc2c, thereby revealing that its pointer type is uint16_t*, meaning its type is uint16_t.

I find this to be more-useful than ptype my_var, but a more direct way to get this effect is desired in case you have any suggestions.

Sample gdb commands and output:

(gdb) ptype my_var
type = unsigned short
(gdb) print &my_var
$27 = (uint16_t *) 0x7ffffffefc2c

Again, notice ptype my_var reveals it is an unsigned short, whereas print &my_var reveals the more-detailed and desired answer which is that it is a uint16_t.