cudaGetLastError After Launch
Catching invalid launch configurations.
cudaGetLastError After Launch is a free CUDA Academy lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the CUDA Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Catching the Silent Launch
Since a kernel launch returns nothing, you need a helper to ask the GPU what just happened. That helper is cudaGetLastError. 🔎
What It Returns
cudaGetLastError hands back the most recent error code recorded by the runtime, or cudaSuccess if everything is fine so far.
myKernel<<<g, b>>>(d);
cudaError_t e = cudaGetLastError();Call It Right After Launch
Place the check on the very next line after the launch. That captures configuration mistakes before any other call overwrites the state.
kernel<<<g, b>>>();
if (cudaGetLastError() != cudaSuccess) abort();It Catches Launch Config Errors
This catches the configuration stage: too many threads per block, zero blocks, or a grid that the device simply cannot accept.
kernel<<<g, 99999>>>(); // invalid thread countIt Clears the Error
Reading the error also resets it to cudaSuccess. The runtime keeps only the last error, so checking it wipes the slate clean.
Peek Without Clearing
Want to look without resetting? Use cudaPeekAtLastError. It returns the same code but leaves the error state untouched.
cudaError_t e = cudaPeekAtLastError();It Does Not Catch Runtime Faults
By itself, this only sees the launch, not the execution. An out-of-bounds access inside the kernel still slips past it.
Pair It With a Sync
To catch runtime faults, follow up with cudaDeviceSynchronize. The launch check plus a sync covers both stages of failure.
kernel<<<g, b>>>();
cudaGetLastError();
cudaDeviceSynchronize();Why Two Checks Help
The launch check tells you the config was valid; the sync tells you the kernel actually finished without crashing. You learn which stage broke.
Wrap It in a Macro
Typing this after every launch gets old. Most projects wrap the launch check in a tidy macro so it is one short line.
kernel<<<g, b>>>();
CHECK_LAUNCH();A Debugging Lifesaver
When a kernel mysteriously does nothing, a quick cudaGetLastError often reveals an invalid launch you would never have spotted otherwise.
Quick Check
Test your grasp of cudaGetLastError.
Recap: Check the Launch
Call cudaGetLastError right after a launch to catch config errors, then sync for runtime faults. Two checks reveal where things broke. 🎉
Frequently asked questions
Is the “cudaGetLastError After Launch” lesson free?
Yes — the full text of “cudaGetLastError After Launch” is free to read here on the web, and the CUDA Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the CUDA Academy course, upgrade to CoddyKit PRO.
What will I learn in “cudaGetLastError After Launch”?
Catching invalid launch configurations. You practise CUDA Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start CUDA Academy?
No prior experience is required. CUDA Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “cudaGetLastError After Launch” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this CUDA Academy lesson?
Yes. Every CUDA Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Return Codes vs Async Errors
- cudaGetLastError After Launch
- A Reusable CUDA_CHECK Macro
- Decoding cudaGetErrorString