Performance Difference Between C and C++ Style File IO

Question

I\'ve always heard that C++ file I/O operations are much much slower then C style I/O. But I didn\'t find any practical references on comparatively how slow they actually ar

Answer 1

No, C++ input/output is not substantially slower than C’s – if anything, a modern implementation should be slightly faster on formatted input/output since it doesn’t need to parse a format string, and the formatting is instead determined at compile time through the chaining of the stream operators.

Here are a few caveats to consider in a benchmark:

• Compile with full optimisations (-O3) to get a fair comparison.
• A proper benchmark needs to estimate biases – in practice this means that you need to repeat your tests and interleave them. At the moment your code isn’t robust to disturbances from background processes. You should also report a summary statistic of the repeated runs to catch outliers that distort the estimates.
• Disable C++ stream synchronisation with C streams (std::ios_base::sync_with_stdio(false);)
• Use '\n' instead of the (flushing) std::endl
• Don’t use register declarations – it simply makes no difference and modern compilers probably ignore it anyway.