I know I can print the n+1-th element of a normal integer array data in GDB as
print *((integer *)data + n)
But how can I correctly print the element out if data is an integer(INT64) allocatable array?
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1 Answer
Note: some older GDB versions or branches used in some unfortunate OSs or distributions may fail to support the allocatable arrays correctly. In that case use the C syntax.
If int64_t isn't recognized by an old GDB, use long or whatever old C type corresponds to a 64-bit integer.
You can really just do
print data(n+1)
Using
print *((integer *)data + n)
is C mode GDB syntax, but in Fortran mode it is really simple.
If you really want the complicated C syntax, you can use it even in Fortran mode, it is
print *((int64_t *)(&data) + n)
In C mode (after set langauge c), you can also use
print *((int64_t *)data + n)
this one does not work in Fortran mode (Cannot access memory at address 0x29).
Example:
use iso_fortran_env
integer(int64), allocatable :: data(:)
integer :: n
data = [(i, i=1, 100)]
n = 5
continue
end
gdb:
GNU gdb (GDB; openSUSE Leap 15.1) 8.3.1
...
(gdb) break int64.f90:9
Breakpoint 1 at 0x4005ec: file int64.f90, line 9.
(gdb) run
Starting program: /home/lada/f/testy/stackoverflow/a.out
Breakpoint 1, MAIN__ () at int64.f90:9
9 n = 5
Missing separate debuginfos, use: zypper install libgcc_s1-gcc10-debuginfo-10.1.1+git68-lp151.27.1.x86_64 libquadmath0-gcc10-debuginfo-10.1.1+git68-lp151.27.1.x86_64
(gdb) step
13 end
(gdb) print data(n+1)
$1 = 6
(gdb) print *((int64_t *)(&data) + n)
$2 = 6
(gdb) set language c
Warning: the current language does not match this frame.
(gdb) print *((int64_t *)data + n)
$3 = 6
(gdb) print *((long *)data + n)
$4 = 6
answered Aug 11, 2020 at 11:45
Vladimir F Героям слава
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6 Comments
Kevin Powell
Unfortunately, ` print data(n+1)` does not work for me and I got
No symbol "int64_t" in current context. when trying to use the C pointer method. I'm using gdb (GDB) 8.0.1 on Mac OS X, not sure whether it is a version problem.Vladimir F Героям слава
@KevinPowell Yes, it is very likely a version problem, please see my note at the very bottom of my answer. If your GDB is that old that it even doesn't understand
int64_t, use just long. Or something else if long does not correspond to 64 bits in your system. But it normally should.Vladimir F Героям слава
Also make sure you are in the Fortran mode (it should be automatic, but you can try
set language fortran). Or in C mode when trying those commands I showed for C mode.Vladimir F Героям слава
@KevinPowell See also stackoverflow.com/questions/50469327/… Apple hates GPLv4 and will not provide any new software version that uses this license. If you want a new version, you have to look elsewhere or compile from original source. Otherwise you have to keep using old methods.
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