C++ unexpected change of members data - c++

Question

One of my class has a trouble: its members data can change unexpectedly.
I have read similar subject on SO, and it seems to be apparent to an undefined behavior or a problem of pointer. But even with a very easy expression of my code, I still have it:
aid.cpp:
#include "aid.h"
bool AID::Detect(t_arr3d x, t_arr3d x_p1, t_arr3d x_p2, t_arr3d x_p3, t_arr3d x_p4, int fp) {
return false;
}
AID::AID() {
this->counter = 0;
maxErrorBound = 0.1;
maxErrorBound2 = 0.02; // = maxErrorBound * lambda
}
aid.h
#ifndef AID_H_
#define AID_H_
#include "detector.h"
#include "vec.h"
#include <map>
#include <vector>
#include <limits>
#include <cstddef>
#include <boost/assign/list_of.hpp>
#include <boost/unordered_map.hpp>
#include "constants.h"
using namespace rode;
using boost::assign::map_list_of;
using namespace std;
class AID: public Detector {
public:
bool Detect(t_arr3d x, t_arr3d x_p1, t_arr3d x_p2, t_arr3d x_p3, t_arr3d x_p4, int fp);
AID();
private:
int counter;
float maxErrorBound ;
float maxErrorBound2;
};
#endif
The class is called in another one (rode.cpp):
...
if(a_detector == "AID"){
AID d = AID( );
this->aid = &d;
}
...
With LLDB, I have put a watchpoint to check what is going on:
Watchpoint 1 hit:
old value: 0
new value: 1606405696
Process 38408 stopped
* thread #1: tid = 0x74cd2, 0x00007fff5fc12171 dyld`ImageLoaderMachO::findExportedSymbol(char const*, bool, ImageLoader const**) const + 13, queue = 'com.apple.main-thread', stop reason = watchpoint 1
frame #0: 0x00007fff5fc12171 dyld`ImageLoaderMachO::findExportedSymbol(char const*, bool, ImageLoader const**) const + 13
dyld`ImageLoaderMachO::findExportedSymbol:
-> 0x7fff5fc12171 <+13>: pushq %rax
0x7fff5fc12172 <+14>: movq %rcx, %r14
0x7fff5fc12175 <+17>: movl %edx, -0x2c(%rbp)
0x7fff5fc12178 <+20>: movq %rsi, %r15
(lldb) bt
* thread #1: tid = 0x74cd2, 0x00007fff5fc12171 dyld`ImageLoaderMachO::findExportedSymbol(char const*, bool, ImageLoader const**) const + 13, queue = 'com.apple.main-thread', stop reason = watchpoint 1
* frame #0: 0x00007fff5fc12171 dyld`ImageLoaderMachO::findExportedSymbol(char const*, bool, ImageLoader const**) const + 13
frame #1: 0x00007fff5fc184f6 dyld`ImageLoaderMachOCompressed::resolveTwolevel(ImageLoader::LinkContext const&, ImageLoader const*, bool, char const*, bool, ImageLoader const**) + 86
frame #2: 0x00007fff5fc18784 dyld`ImageLoaderMachOCompressed::resolve(ImageLoader::LinkContext const&, char const*, unsigned char, long, ImageLoader const**, ImageLoaderMachOCompressed::LastLookup*, bool) + 276
frame #3: 0x00007fff5fc1a09b dyld`ImageLoaderMachOCompressed::doBindFastLazySymbol(unsigned int, ImageLoader::LinkContext const&, void (*)(), void (*)()) + 235
frame #4: 0x00007fff5fc0424e dyld`dyld::fastBindLazySymbol(ImageLoader**, unsigned long) + 90
frame #5: 0x00007fff9610b3ba libdyld.dylib`dyld_stub_binder + 282
frame #6: 0x000000010004f268 wrf2sl`GCC_except_table678 + 3660
frame #7: 0x00000001000270f9 wrf2sl`main(argc=15, argv=0x00007fff5fbffaa0) + 21337 at wrf2sl.cc:170
frame #8: 0x00007fff9610d5c9 libdyld.dylib`start + 1
wrf2sl is my program. But the rest is not related to it.
Have you ever seen a similar trouble?
How should I check to understand what is going on?

Answer 1

The problem is here
if(a_detector == "AID"){
AID d = AID( );
this->aid = &d;
}
Here you create a local variable in the scope of the if body, and it's local only inside there. Then you store a pointer to that local variable, a pointer to an object that is destructed once the if statement is done. That will lead to undefined behavior when you try to dereference the pointer to a non-existent object.
My advice is to not use pointers to start with, and instead store the object as a value (i.e. an actual instance of the AID class). If you must use pointers, then allocate it dynamically with new, and remember to delete it when you're done with it (or optionally depending on use-case use a smart pointer).