What's the time complexity of character array initialization?

Question

As usually reading through stuff I got this question in mind. If I have a character array initialization like below , what will be the time complexity for this statement?

char array[] = {'a','b','c','d','e'};

Will it actually execute 5 time to assign each variable; as we do in loop. If assumption is true why is it so?

Answer 1

depending on where the declaration occurs and the compiler's intelligence, it could be O(1) or O(n). some cases:

1. global declaration, smart compiler would put it in data section, already initialized, thus O(1)
2. local declaration, if proven to be read only by a smart compiler, it could be like above, plus a reference assignment to the array, still O(1) however
3. local declaration, read write, could be storage allocation + 5 assignment (clearly O(n) OR storage allocation + array data copy (like 2, but the data gets copied instead of only the reference). the latter could be O(1) with vectorized code (well... more or less because it depends on quite a lot of things)

Answer 2

It's O(N). It might be a fast or efficient O(N). And if it's a statically allocated array, the initialization will only be done once.

But in any case, it's O(N).

Note that even if it's an array that's placed in the binary image of the program (because the compiler determines that the array is never modified), it's still an O(N) operation to initialize it, even though the initialization might occur before the program event reaches main() or is done as part of the program image load.

It's O(N) because whatever does the initialization has to write to each location of the array, so an array that's 100 times as long as another will have on the order of 100 times more operations to perform to complete the initialization.