Using C object files in Delphi is hard but possible. Linking to C++ object files is, however, nearly impossible. The problem does not lie within the object files themselves, but in C++.

While C is hardly more than an assembler with improved syntax, C++ represents a sophisticated high-level language with runtime support for strings, objects, exceptions, and more. All these features are part of almost any C++ program and are as such compiled into (almost) any object file produced by C++.

The problem here is that Delphi has no idea how to deal with any of that. A C++ object is not equal to a Delphi object. Delphi has no idea how to call functions of a C++ object, how to deal with its inheritance chain, how to create and destroy such objects, and so on. The same holds for strings, exceptions, streams, and other C++ concepts.

If you can compile the C++ source with C++Builder then you can create a package (.bpl) that can be used from a Delphi program. Most of the time, however...