How to print first n lines of a variable with GDB?

Question

While debugging with GDB, I have a really large variable that I would like to print. However, only first n lines should be printed. How can I print the first n lines with the "print" GDB command? Like a "head" command in Linux.

In particular, the variable is a structure / record.

Answer 1

If you have a GDB that supports Ada, and assuming that very large means an array, then use slices.

(gdb) p x(1..3)
$2 = ((first => 0, second => 0), (first => 0, second => 0), (first => 0, second => 0))
(gdb) p x(1..5)
$3 = ((first => 0, second => 0), (first => 0, second => 0), (first => 0, second => 0), (first => 0, second => 0), (first => 0, second => 0))
(gdb) 

If it is a record, accessing the components will reduce output:

(gdb) p y.x  
$2 = (a => 0 '["00"]', b => 0 '["00"]', c => 0 '["00"]', d => 0 '["00"]')
(gdb) p y.x.a
$3 = 0 '["00"]'
(gdb) 

Otherwise, gdb, if run from on the command line shell, may pipe to more(1) on UNIX; from within Emacs, all kinds of output processing are made possible, insofar as GDB outputs text.