How to calculate the length of output that sprintf will generate?

Question

Goal: serialize data to JSON.

Issue: i cant know beforehand how many chars long the integer is.

i thought a good way to do this

Answer 1

This isn't strictly an answer to your question, but you may find it helpful nonetheless. It is not portable, but if you're running this on glibc, you can simply use asprintf() instead, which will do the memory allocation for you.