How to debug segmentation fault?

Question

It works when, in the loop, I set every element to 0 or to entry_count-1. It works when I set it up so that entry_count is small, and I write it by hand instead of by loop (

Answer 1

This is clearly a symptoms of invalid memory uses within your program.This would be bit difficult to find by looking out your code snippet as it is most likely be the side effect of something else bad which has already happened.

However as you have mentioned in your question that you are able to attach your program using Valgrind. as it is reproducible. So you may want to attach your program(a.out).

$ valgrind --tool=memcheck --db-attach=yes ./a.out

This way Valgrind would attach your program in the debugger when your first memory error is detected so that you can do live debugging(GDB). This should be the best possible way to understand and resolve your problem.

Once you are able to figure it out your first error, fix it and rerun it and see what are other errors you are getting.This steps should be done till no error is getting reported by Valgrind.

However you should avoid using the raw pointers in modern C++ programs and start using std::vector std::unique_ptr as suggested by others as well.