My guess is that it is a problem with the compiler options you are using, the compiler itself, or the file system. I just now compiled both versions (with optimizations on) and ran them against a 92,000 line text file:
c++ version: 113 ms
c version: 179 ms
And I suspect that the reason that the C++ version is faster is because fgetc is most likely slower. fgetc does use buffered I/O, but it is making a function call to retrieve every character. I’ve tested it before and fgetc is not as fast as making a call to read the entire line in one call (e.g., compared to fgets).