How much performance difference when using string vs char array?

Question

I have the following code:

char fname[255] = {0}
snprintf(fname, 255, \"%s_test_no.%d.txt\", baseLocation, i);

vs

std::stri         


        

Answer 1

If it's REALLY important, measure the two solutions. If not, whichever you think makes most sense from what data you have, company/private coding style standards, etc. Make sure you use an optimised build [with the same optimisation you are going to use in the actual production build, not -O3 because that is the highest, if your production build is using -O1]

I expect that either will be pretty close if you only do a few. If you have several millions, there may be a difference. Which is faster? I'd guess the second [1], but it depends on who wrote the implementation of snprintf and who wrote the std::string implementation. Both certainly have the potential to take a lot longer than you would expect from a naive approach to how the function works (and possibly also run faster than you'd expect)

[1] Because I have worked with printf, and it's not a simple function, it spends a lot of time messing about with various groking of the format string. It's not very efficient (and I have looked at the ones in glibc and such too, and they are not noticeably better). On the other hand std::string functions are often inlined since they are template implementations, which improves the efficiency. The joker in the pack is whether the memory allocation for std::string that is likely to happen. Of course, if somehow baselocation turns to be rather large, you probably don't want to store it as a fixed size local array anyway, so that evens out in that case.