Converting double to char* in C++ with high performance

Question

My application needs to convert double values to char* to write to a pipe that accepts only characters. The usual ways of doing this are using the sprintf() functio

Answer 1

The slow part of sprintf on your system may not necessarily be converting the double, but parsing the format string. That might be good news for you as that is something that you could optimize away.

Additionally, try hard to document all the knowledge you have about range, accuracy, and nature of the double values that you need to process, and use it to develop a special algorithm.

Assuming your inputs are never subnormal numbers, use a known fixed precision and accuracy, a relatively high performing result may look like this:

itoa((int)((f + 0.00001) * 10000))

However, the sprintf and ostream approaches you are already aware of are the only solutions that are completely general and portable.