diff --git a/CppCoreGuidelines.md b/CppCoreGuidelines.md index 69b17fc..2a4549c 100644 --- a/CppCoreGuidelines.md +++ b/CppCoreGuidelines.md @@ -12325,7 +12325,6 @@ Don't replicate the work of others. Benefit from other people's work when they make improvements. Help other people when you make improvements. -**References**: ??? ### SL.2: Prefer the standard library to other libraries @@ -12334,10 +12333,64 @@ Help other people when you make improvements. More people know the standard library. It is more likely to be stable, well-maintained, and widely available than your own code or most other libraries. + ## SL.con: Containers +* [SL.10: Prefer using STL `array` or `vector` instead of a C array](#Rsl-arrays) +* [SL.11: Prefer using STL `vector` by default unless you have a reason to use a different container](#Rsl-vector) ??? +### SL.10: Prefer using STL `array` or `vector` instead of a C array + +##### Reason + +C arrays are less safe, and have no advantages over `array` and `vector`. +For a fixed-length array, use `std::array`, which does not degenerate to a pointer when passed to a function and does know its size. +For a variable-length array, use `std::vector`, which additionally can change its size and handles memory allocation. + +##### Example + + int v[SIZE]; // BAD + + std::array w; // ok + +##### Example + + int* v = new int[initial_size]; // BAD, owning raw pointer + delete[] v; // BAD, manual delete + + std::vector w(initial_size); // ok + +##### Enforcement + +* Flag declaration of a C array inside a function or class that also declares an STL container (to avoid excessive noisy warnings on legacy non-STL code). To fix: At least change the C array to a `std::array`. + + +### SL.11: Prefer using STL `vector` by default unless you have a reason to use a different container + +##### Reason + +`vector` and `array` are the only standard containers that offer the fastest general-purpose access (random access, including being vectorization-friendly), the fastest default access pattern (begin-to-end or end-to-begin is prefetcher-friendly), and the lowest space overhead (contiguous layout has zero per-element overhead, which is cache-friendly). Usually you need to add and remove elements from the container, so use `vector` by default; if you don't need to modify the container's size, use `array`. + +Even when other containers seem more suited, such a `map` for O(log N) lookup performance or a `list` for efficient insertion in the middle, a `vector` will usually still perform better for containers up to a few KB in size. + +##### Note + +`string` should not be used as a container of individual characters. A `string` is a textual string; if you want a container of characters, use `vector` or `array` instead. + +##### Exceptions + +If you have a good reason to use another container, use that instead. For example: + +* If `vector` suits your needs but you don't need the container to be variable size, use `array` instead. + +* If you want a dictionary-style lookup container that guarantees O(K) or O(log N) lookups, the container will be larger (more than a few KB) and you perform frequent inserts so that the overhead of maintaining a sorted `vector` is infeasible, go ahead and use an `unordered_map` or `map` instead. + +##### Enforcement + +* Flag a `vector` whose size never changes after construction (such as because it's `const` or because no non-`const` functions are called on it). To fix: Use an `array` instead. + + ## SL.str: String ???