[pjmlp]

Depends how C++ compatible are the headers, as they can't make use of C99 or C11 features that aren't part of ANSI C++17.

[jjnoakes]

True, although most C libraries ought to use those features in the implementation files and not the headers if they want to be used widely.

And even if some things leak into the headers they might be accepted by compiler extensions.

But yes, in general if a c library's headers are hostile to cross-language usage then using it from c++ won't be trivial.