ใช้ cudaGetLastError หลังการเรียกใช้

Since a kernel launch returns nothing, you need a helper to ask the GPU what just happened. That helper is cudaGetLastError. 🔎

cudaGetLastError hands back the most recent error code recorded by the runtime, or cudaSuccess if everything is fine so far.

Place the check on the very next line after the launch. That captures configuration mistakes before any other call overwrites the state.

This catches the configuration stage: too many threads per block, zero blocks, or a grid that the device simply cannot accept.

Reading the error also resets it to cudaSuccess. The runtime keeps only the last error, so checking it wipes the slate clean.

Want to look without resetting? Use cudaPeekAtLastError. It returns the same code but leaves the error state untouched.

By itself, this only sees the launch, not the execution. An out-of-bounds access inside the kernel still slips past it.

To catch runtime faults, follow up with cudaDeviceSynchronize. The launch check plus a sync covers both stages of failure.

The launch check tells you the config was valid; the sync tells you the kernel actually finished without crashing. You learn which stage broke.

Typing this after every launch gets old. Most projects wrap the launch check in a tidy macro so it is one short line.

When a kernel mysteriously does nothing, a quick cudaGetLastError often reveals an invalid launch you would never have spotted otherwise.

Test your grasp of cudaGetLastError.

Call cudaGetLastError right after a launch to catch config errors, then sync for runtime faults. Two checks reveal where things broke. 🎉