strtok() happily punches those holes in. Now you could argue, the resulting strings, while null-terminated, aren't true substrings (as the origin string is now corrupted), but in the context of parsing (particularly here using white-space as delimiter), that wouldn't be much an issue.

Struct Substring { char start, end };

My point is ownership being transferred implicitly in a struct assignment is a complexity introduced by C++.

In C the concern of allocating memory and using it is separate.

String_view is attempt to add more separation. But C programmers were already there.

Well yeah, and you could always do the same thing in C++, but having a standard structure for it makes interoperability a lot easier.

An object of type char * isn't necessarily null-terminated.

No, but that makes it no longer a string as far as most C functions are concerned.