C Arrays vs. Vectors: When Do Performance Differences Matter?

Performance Differences in C Arrays and Vectors

In modern C programming, it's generally recommended to use std::vectors instead of C arrays. While both provide means of data storage, there are subtle performance differences to consider.

C Arrays

C arrays, particularly when allocated dynamically using new, can lead to memory management issues. You need to manually track size and perform explicit deletion, resulting in additional housekeeping overhead.

std::Arrays

std::arrays provide a wrapper around C arrays, adding features like size determination and iterators. However, like C arrays, they have limitations when passed as arguments, as they are converted to pointers and lose their size information.

std::Vectors vs. Native C Arrays

Detailed analysis of assembly code reveals that indexing and dereferencing operations on std::vectors perform comparably to C arrays and pointers. Incrementing vector iterators also has the same performance as incrementing pointers.

However, there are exceptions to this general rule. When constructing std::vectors with non-class objects or classes lacking a user-defined constructor and without initial element initialization, new-allocated C arrays may offer performance advantages. This is because std::vectors initialize all elements by default on construction.

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