This will be obvious to any C programmer, but the macro[1] used throughout the article only "works" on string literals and arrays, not pointers.

Also, it will include the null terminator. Probably won't do any harm but quite silly if you're redirecting to a file for example. I'd subtract one, or use strlen which would cover the pointer case above and I'd hope a modern compiler would elide the call on a string literal anyway.

[1] #define szstr(str) str,sizeof(str)