Is std::vector so much slower than plain arrays?

Question

I\'ve always thought it\'s the general wisdom that std::vector is \"implemented as an array,\" blah blah blah. Today I went down and tested it, and it seems to

Answer 1

My laptop is Lenova G770 (4 GB RAM).

The OS is Windows 7 64-bit (the one with laptop)

Compiler is MinGW 4.6.1.

The IDE is Code::Blocks.

I test the source codes of the first post.

The results

O2 optimization

UseArray completed in 2.841 seconds

UseVector completed in 2.548 seconds

UseVectorPushBack completed in 11.95 seconds

The whole thing completed in 17.342 seconds

system pause

O3 optimization

UseArray completed in 1.452 seconds

UseVector completed in 2.514 seconds

UseVectorPushBack completed in 12.967 seconds

The whole thing completed in 16.937 seconds

It looks like the performance of vector is worse under O3 optimization.

If you change the loop to

    pixels[i].r = i;
    pixels[i].g = i;
    pixels[i].b = i;

The speed of array and vector under O2 and O3 are almost the same.