I’ve been informed that my library is slower than it should be, on the order of 30+ times too slow parsing a particular file (text file, size 326 kb). The user suggested that it may be that I’m using std::ifstream (presumably instead of FILE).
I’d rather not blindly rewrite, so I thought I’d check here first, since my guess would be the bottleneck is elsewhere. I’m reading character by character, so the only functions I’m using are get(), peek(), and tellg()/seekg().
Update:
I profiled, and got confusing output – gprof didn’t appear to think that it took so long. I rewrote the program to read the entire file into a buffer first, and it sped up by about 100x. I think the problem may have been the tellg()/seekg() that took a long time, but gprof may have been unable to see that for some reason. In any case, ifstream does not appear to buffer the entire file, even for this size.
I don’t think that’d make a difference. Especially if you’re reading char by char, the overhead of I/O is likely to completely dominate anything else. Why do you read single bytes at a time? You know how extremely inefficient it is?
On a 326kb file, the fastest solution will most likely be to just read it into memory at once.
The difference between std::ifstream and the C equivalents, is basically a virtual function call or two. It may make a difference if executed a few tens of million times per second, otherwise, not reall. file I/O is generally so slow that the API used to access it doesn’t really matter. What matters far more is the read/write pattern. Lots of seeks are bad, sequential reads/writes good.