Unfortunately there are still cases where the A API has bugs that the W API lacks, see e.g: https://stackoverflow.com/q/67427569 https://stackoverflow.com/q/674

Unfortunately there are still cases where the A API has bugs that the W API lacks, see e.g: https://stackoverflow.com/q/67427569 https://stackoverflow.com/q/67427569 Also, some APIs use buffers with a fixed maximum size, and the A API's buffer isn't big enough to handle the maximum possible data size for the W API. And some APIs are Unicode-only, and don't have A versions. For maximum reliability, better to use W APIs only and do the UTF-8<->UTF-16 conversion yourself. However, in practice, if you just use A APIs only and let Windows do the UTF-8 conversion for you, it is going to work 95% of the time. But maybe at some point you'll hit that 5% where it doesn't. It is more likely if you are using more obscure APIs (like my example at the start of manipulating Windows Terminal Server sessions). More likely for system-level stuff than application-level.