Is std::vector Significantly Slower Than Plain Arrays in Practice?

Does std::vector Perform Significantly Slower than Plain Arrays?

In a benchmark comparison, the performance gap between std::vector and plain arrays has been a topic of debate. While it is commonly believed that std::vector implements an array, recent tests have shed light on the potential performance differences between the two.

Benchmark Results and Observations

Initial tests revealed a significant performance disparity, with std::vector completing three to four times slower than plain arrays. However, upon further scrutiny, the reason for this discrepancy became evident.

In the original code, the std::vector underwent two iterations within the test loop, leading to a doubling of the access time. By optimizing the code to execute the vector's initialization only once, the performance gap narrowed considerably.

Optimized Code Results

Using the following optimized code:

std::vector<Pixel> pixels(dimensions * dimensions, Pixel(255, 0, 0));

the performance of std::vector dropped significantly, now performing only slightly slower than the plain array. This suggests that under optimized conditions, the performance differences between the two data structures are minimal.

Additional Considerations

When comparing std::vector and plain arrays, it is crucial to highlight that the PlainArray() method did not properly initialize nor destruct the Pixel objects. While this may not pose significant issues for simple objects like Pixel, it can lead to complications for more complex objects, particularly those involving pointers.

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