Is C code still considered C++?

Question

The comment to this answer got me wondering. I've always thought that C was a proper subset of C++, that is, any valid C code is valid C++ code by extension. Am I wrong about that? Is it possible to write a valid C program that is not valid C++ code?

EDIT: This is really similar to, but not an exact duplicate of this question.

Answer 1

In general, yes C code is considered C++ code.

But C is not a proper subset in a strict sense. There are a couple of exceptions.

Here are some valid things in C that are not valid in C++:

int *new;//<-- new is not a keyword in C
char *p = malloc(1024); //void * to char* without cast 

There are more examples too, but you get the idea.

I previously wrote a more extensive answer in a similar question here.

Answer 2

Also note that C99 adds several features which aren't permitted in C++ (or are only supported using vendor extensions), such as builtin _Complex and _Imaginary data types, variable-length arrays (arrays sized at runtime rather than compile time), flexible array members (arrays declared as the last member of a struct that may contain an unspecified number of elements), and more.

For the exhaustive list of incompatibilities between C and C++, including changes with C99, see http://david.tribble.com/text/cdiffs.htm.