C++ is as close as possible to compatible with C, but no closer. In practice, the major difference is that C++ requires prototypes, and that
f()declares a function that takes no parameters (in C, a function declared using
f()can be passed an arbitrary number of parameters of arbitrary types).
There are some very subtle differences as well, like
sizeof('x')is equal to
sizeof(char)in C++ but is equal to
sizeof(int)in C. Also, C++ puts structure “tags” in the same namespace as other names, whereas C requires an explicit
typedef struct Fred Fred;technique still works, but is redundant in C++).