How to Fix “Attempting to write outside the bounds of a buffer” in GameMaker

Binary save and network code hits this when layout assumptions drift. The write side and read side must be the same code shape — or the same code. Here is the discipline.

How to fix it

1. Prefer buffer_grow for variable data

Fixed buffers (buffer_fixed) error at the boundary; buffer_create(1024, buffer_grow, 1) expands on write — right for saves whose size varies with progress.

2. Mirror write and read exactly

Every buffer_write(buf, buffer_u16, ...) must pair with a same-type, same-order read — a single u8/u16 mismatch shifts every following field and eventually overruns.

3. Length-prefix collections

Write counts before arrays and lengths before strings so readers know exactly how much to consume — never infer from total size.

4. Version the format

A version byte at the head lets new code read old saves deliberately instead of misparsing them into bounds errors on players' machines.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every GameMaker error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.