Re: GDB can't parse variables named "memory" or "array"?

[Paul Smith <paul at mad-scientist dot net>]

On Fri, 2017-09-29 at 14:57 -0400, Sergio Durigan Junior wrote:
> On Friday, September 29 2017, Paul Smith wrote:
> > I've tried this with lots of different versions of GDB (7.7.1,
> > 7.11, 7.12, etc.), and none of them work when debugging my programs
> > (not just my main program but all my unit tests as well):
> > 
> >    (gdb) p memory
> >    A syntax error in expression, near `'.
> > 
> >    (gdb) p array
> >    A syntax error in expression, near `'.

> You can also enable "set debug parser on" and/or "set debug
> expression 1" inside your "faulty" GDB and see if it helps with
> anything.

This gave very useful information, actually.  I now see what's
happening, although I can't understand why no one has noticed this so
I'm not sure.

Printing "array" or "memory" shows:

  (gdb) p memory
  Starting parse
  Entering state 0
  Reading a token: Next token is token FILENAME (bval<0x335a1d0>)
  Shifting token FILENAME (bval<0x335a1d0>)
  Entering state 47
  Reducing stack by rule 107 (line 932):
     $1 = token FILENAME (bval<0x335a1d0>)
  -> $$ = nterm block ()
  Stack now 0
  Entering state 57
  Reading a token: Now at end of input.
  A syntax error in expression, near `'.

The problem appears to be with the C++ header files, which don't have
extensions.  Here's a repro case:

$ cat gdbtest.cpp
// must include memory
#include <memory>

class Foo
{
    char* memory;
};

Foo foo;

int main(int, char**)
{
    return 1;
}

$ g++ --ggdb3 -o gdbtest gdbtest.cpp

$ gdb -n gdbtest
 ...
(gdb) br 13
(gdb) run
(gdb) p foo.memory
A syntax error in expression, near `'.


Note that you have to use -ggdb3 to see the problem; just using -g
doesn't show the error.  Also it ends up that the symbol must be part
of a class (or probably struct but not tested): if it's a global or
auto symbol it's interpreted correctly.

Why is GDB even considering a filename to be part of a print
expression?