C Arrays vs. std::vectors: Which Offers Superior Performance?

Performance Comparison of C Arrays and std::Vectors

In C , the choice between using arrays and std::vectors has been debated, with varying opinions on performance implications. This article aims to shed light on this topic, exploring the differences between the two and evaluating their performance characteristics.

Avoidance of Dynamic Arrays and Stack Arrays

Modern C practices recommend against using dynamic arrays, as they require manual memory management and size tracking, leading to potential bugs and errors. Stack arrays, while faster than dynamic arrays, lack runtime bounds checking and lose size information upon conversion to pointers, making them suitable only for small, fixed-size allocations.

std::array vs. Stack Arrays

For small, fixed-size allocations, std::array provides a preferred solution over stack arrays. It encapsulates a C array in a small class, offering range checking, iterators, and a size function.

std::Vectors vs. Native C Arrays

Contrary to common misconceptions, accessing elements in std::vectors using the [] operator or iterators incurs no significant performance overhead compared to accessing elements in native C arrays. The underlying assembly instructions for index access and pointer dereferencing are identical.

int pointer_index(S& s) { return s.p[3]; } // Equivalent to std::vector access
int vector_index(S& s) { return s.v[3]; } // Identical assembly code

Incrementing vector iterators or pointers also exhibits no performance difference.

void pointer_increment(S& s) { ++s.p; } // Equivalent to iterator increment
void iterator_increment(S& s) { ++s.i; } // Identical assembly code

Exceptions

One notable exception to the equivalent performance is the initialization of elements. If memory is allocated for an array with new without user-defined constructors, data is not initialized, while std::vectors initialize all elements to their default values (e.g., 0 for integers) upon construction. This difference can translate to performance benefits if element initialization is required.

Conclusion

While C arrays and std::vectors have distinct characteristics, their performance characteristics for basic operations are essentially identical. std::vectors provide additional features such as bounds checking and iterators, making them the preferred choice for most modern C development scenarios.

The above is the detailed content of C Arrays vs. std::vectors: Which Offers Superior Performance?. For more information, please follow other related articles on the PHP Chinese website!