You could use win32 functions that parse .ini files. (Better for programming efficiency) But if you do write your own parser, C++ streams ought achieve similar results as C io streams.But some implementations might require you to setup the streams specially to achieve the best speed. Read your C++ iostreams library documentation.
I am starting to write a parser for a ini file for a friend as a learning experience. They told me that for file IO that streaming is not as good as using the fopen/fclose or win32 api file IO. I was curious why this was, they would never really supply a decent answer and it seemed like they said that because of preference, but I wanted to check with a resource of more experience programmers.