C++中文周刊周末圆桌讨论 1124

## 代码鉴赏 string_view和char *混用
                        ```C++
                            #include  <iostream>
                            #include <string_view>
                            void print_me(std::string_view s) {
                                printf("%s\n", s.data());
                            }
                            
                            int main() {
                              char next[] = {'n','e','x','t'};
                              char hello[] = {'H','e','l','l','o', ' ',
                                              'W','o','r','l','d'};
                              std::string_view sub(hello, 5);
                              std::cout << sub << "\n";
                              print_me(sub);
                            }
                        ```
                        - 表面不炸没准哪天就炸了
                        - 记得facebook有个类似的问题， https://www.youtube.com/watch?v=kPR8h4-qZdk&t=1150s
                        - sanitize能抓到
                        - 注意转换问题，string string_view char * char[] vector u8

## [hardening mode](https://libcxx.llvm.org/Hardening.html)
                        - [设计文档](https://discourse.llvm.org/t/rfc-hardening-in-libc/73925)
                        - 已有实践 [google](https://security.googleblog.com/2024/11/retrofitting-spatial-safety-to-hundreds.html) 性能下降1%
                            - 他们测试数据性能影响不到1%，非常可观
                            - 加固只有1% 3%性能损失？
                        > While these new runtime safety checks improve security, they add additional runtime overhead and can negatively impact performance. 
                        > We studied the performance degradation for Google workloads and Feedback Direct Optimization (FDO) proved to be effective in minimizing it. 
                        > As an example, enabling the hardened libc++, without any FDO, 
                        > in a representative Google fleet workload added a ~0.9% queries per second (QPS) regression and a ~2.5% latency regression. 
                        > When properly using FDO, we measured a ~65% reduction in QPS overhead and a ~75% reduction in latency overhead.

| Category name 分类名称        | `fast` | `extensive` | `debug` |
                        | ------------------------------------ | --------- | ----------------- | -------- |
                        | `valid-element-access`    | ✅                                  | ✅                                       | ✅                                   |
                        | `valid-input-range`       | ✅                                  | ✅                                       | ✅                                   |
                        | `non-null`                | ❌                                  | ✅                                       | ✅                                   |
                        | `non-overlapping-ranges`  | ❌                                  | ✅                                       | ✅                                   |
                        | `valid-deallocation`      | ❌                                  | ✅                                       | ✅                                   |
                        | `valid-external-api-call` | ❌                                  | ✅                                       | ✅                                   |
                        | `compatible-allocator`    | ❌                                  | ✅                                       | ✅                                   |
                        | `argument-within-domain`  | ❌                                  | ✅                                       | ✅                                   |
                        | `pedantic`                | ❌                                  | ✅                                       | ✅                                   |
                        | `semantic-requirement`    | ❌                                  | ❌                                       | ✅                                   |
                        | `internal`                | ❌                                  | ❌                                       | ✅                                   |
                        | `uncategorized`           | ❌                                  | ✅                                       | ✅                                   |

| Name 姓名                                        | Member functions 成员函数 | Iterators (ABI-dependent)迭代器（与 ABI 相关） |
                        | --------------------------------------------------- | ---------------------------- | ------------------------------------------------ |
                        | `span`               | ✅                         | ✅                                             |
                        | `string_view`        | ✅                         | ✅                                             |
                        | `array`              | ✅                         | ❌                                             |
                        | `vector`             | ✅                         | ✅ (see note) ✅（参见备注）                  |
                        | `string`             | ✅                         | ✅ (see note) ✅（参见备注）                  |
                        | `list`               | ✅                         | ❌                                             |
                        | `forward_list`       | ❌                         | ❌                                             |
                        | `deque`              | ✅                         | ❌                                             |
                        | `map`                | ❌                         | ❌                                             |
                        | `set`                | ❌                         | ❌                                             |
                        | `multimap`           | ❌                         | ❌                                             |
                        | `multiset`           | ❌                         | ❌                                             |
                        | `unordered_map`      | Partial 部分              | Partial 部分                                  |
                        | `unordered_set`      | Partial 部分              | Partial 部分                                  |
                        | `unordered_multimap` | Partial 部分              | Partial 部分                                  |
                        | `unordered_multiset` | Partial 部分              | Partial 部分                                  |
                        | `mdspan`             | ✅                         | ❌                                             |
                        | `optional`           | ✅                         | N/A /无/                                      |
                        | `function`           | ❌                         | N/A /无/                                      |
                        | `variant`            | N/A /无/                  | N/A /无/                                      |
                        | `any`                | N/A /无/                  | N/A /无/                                      |
                        | `expected`           | ✅                         | N/A /无/                                      |
                        | `valarray`           | Partial 部分              | N/A .无可用信息                               |
                        | `bitset`             | ❌                         | N/A /无/                                      |