How to use Gdb debugger to find value of ZZ object from Number Theory Library?

Question

I use gdb debugger to print values of a variable which is of type ZZ. This data type is defined in Number Theory Library or NTL. When I use "print x" to find out my variable's value I obtain something like this:

print x 
$1 = {rep=0xab2cc54}. 

I guess this is the address of my ZZ object. How can I print its value ? I should mention that I don't know the internal representation of this class.

Can I use NTL with a compiler like Eclipse to debug easier my application ?

Answer 1

… my ZZ object. How can I print its value ?

This is a bit ugly, but works:

(gdb) call NTL::operator<<(std::ostream&, NTL::ZZ const&)(cerr, x)
42$1 = (std::ostream &) @0x620020: <incomplete type>

(in this example, the variable x has the value 42).
If you don't want the garbage after the value, you can cast to void:

(gdb) call (void)NTL::operator<<(std::ostream&, NTL::ZZ const&)(cerr, x)
42(gdb) 

(but note that then there's no newline after the value).

If you're not using namespace std, you may have to write

(gdb) call NTL::operator<<(std::ostream&, NTL::ZZ const&)('std::cerr', x)

Sometimes cerr may not be in scope:

(gdb) call NTL::operator<<(std::ostream&, NTL::ZZ const&)(cerr, x)        
No symbol "cerr" in current context.

- then you can try with cout, but it gets even uglier, because the buffered output has to be flushed:

(gdb) call NTL::operator<<(std::ostream&, NTL::ZZ const&)(cout, x)
(gdb) call 'std::basic_ostream<char, std::char_traits<char>>& std::operator<< <std::char_traits<char>>(std::basic_ostream<char, std::char_traits<char>>&, char const*)'(&cout, "\n")
42

Answer 2

Can I use NTL with a compiler like Eclipse ...

First off: Eclipse isn't a compiler but an IDE that encapsulates compiler and debugging facilities for you.

In debugging mode the IDE is capable to resolve the actual types and inner representation used from your source code and letting you walk through.

That said I'm pretty sure you can use Eclipse CDT, to inspect your specific type values.