The crash site may follow the original damage
On Windows, an access violation indicates an invalid memory read, write, or execution attempt. The instruction that stops need not be the one that introduced the problem. An earlier out-of-bounds write can damage a pointer used much later. Before changing the crashing line or adding a null check, establish what memory access was attempted. Operating systems and debuggers can present exceptions differently, so read the stop reason, signal name, and GDB output together. Continuing immediately can lose the clearest view of the first failure.
Reconstruct the accessed address
Read the current instruction and identify whether it reads or writes memory. Determine whether the address comes from one register or from a base, index, and offset. A small invalid address can suggest a null base plus a field offset, but that is a hypothesis rather than proof. Track where the relevant register obtained its value. Compare the access size with the expected object boundaries as well as the address itself. These details are more useful than searching only for the numeric error code.
Check the caller’s contract
When the stop is inside a copy or file routine, inspect the caller that provided the pointer and length. Is length measured in characters or bytes? Does it include a terminator? Is it within the destination capacity? Failure at a particular input size makes boundary arithmetic worth checking. Record the input and build as well as the address. An address can change in another run, while the file contents and length that trigger the calculation remain useful reproduction conditions.
Find the earlier write
Reduce the failing input where possible so that allocation and writes are easier to follow. AddressSanitizer can help identify out-of-bounds access or use-after-free when the toolchain supports it. DBG Desk does not diagnose every memory error automatically. Its stop view supplies observations; a fix should explain the broken lifetime or boundary condition. Re-run the failing input and nearby sizes after a change rather than checking only that one crash disappears.
Keep a pair of boundary inputs
If a file record of length 15 succeeds and one of length 16 fails, preserve both. Compare buffer capacity and terminator handling at the same stop. Use safe synthetic data before sharing a reproduction. A good record explains how to reach the invalid logical access even when its numeric address changes between sessions.