C 中文周刊 第105期
周刊项目地址
弄了个qq频道，手机qq点击进入
RSS https://github.com/wanghenshui/cppweeklynews/releases.atom
欢迎投稿，推荐或自荐文章/软件/资源等
资讯
标准委员会动态/ide/编译器信息放在这里
编译器信息最新动态推荐关注hellogcc公众号 本周更新 2023-03-15 第193期
线下聚会了说是
文章
- Effortless Performance Improvements in C : std::string_view
TLDR 尽可能使用string_view替代std::string，速度提升显著
- 如何扩展asio
扩展思路
- sonic-cpp
字节跳动一个json库，兼顾速度和好用，可以关注一波
- User-Defined Literals To Handle Units
介绍用户自定义字符操作符的
比如 ms，再比如
代码语言：javascript复制long double operator""_deg_to_rad(long double deg)
{
long double radians = deg * std::numbers::pi_v<long double> / 180;
return radians;
}
// ...
// value is now 90 degree in radiants -> 1.5707...
double value = 90.0_deg_to_rad;- Combining Collections with Zip in C 23 for Efficient Data Processing
#include <format>
#include <iostream>
#include <ranges>
#include <vector>
int main() {
std::vector a { 10, 20, 30, 40, 50 };
std::vector<std::string> b { "one", "two", "three", "four" };
for (const auto& [num, name] : std::views::zip(a, b))
std::cout << std::format("{} -> {}n", num, name);
}zip介绍的文章，c 23可用
- Iterating and inverting a const views::filter
constexpr auto isPrint = [](auto c) { return std::isprint(c); };
constexpr auto isXDigit = [](auto c) { return std::isxdigit(c); };
constexpr auto hexdigital = std::views::filter(isXDigit);
constexpr auto printable = std::views::filter(isPrint);
constexpr auto digits = std::views::iota(' ')
| std::views::take(256)
| hexdigital;
for (char c : digits) ~~~ // Error
for (char c : digits | printable) ~~~ // Error报错真么办，本质上，digits这里的遍历不是const，只能decay，c 23用auto解决
代码语言：javascript复制for (char c : auto(digits)) ~~~ // OK
for (char c : auto(digits) | printable) ~~~ // OK另外，反转，直接贴代码
代码语言：javascript复制constexpr auto rest = [](auto fv) {
return fv.base() | std::views::filter(std::not_fn(fv.pred()));
};
for (char c : rest(digits)) ~~~ // OK
for (char c : rest(digits) | printable) ~~~ // OK- Runtime asserts are not free
大概慢几倍。当然发现bug最重要
- Trimming spaces from strings faster with SVE on an Amazon Graviton 3 processor
写了个针对arm sve指令的trim优化
原版
代码语言：javascript复制size_t trimspaces(const char *s, size_t len, char *out) {
char * init_out{out};
for(size_t i = 0; i < len; i ) {
*out = s[i];
out = (s[i] != ' ');
}
return out - init_out;
}改进
代码语言：javascript复制size_t sve_trimspaces(const char *s, size_t len, char *out) {
uint8_t *out8 = reinterpret_cast<uint8_t *>(out);
size_t i = 0;
for (; i svcntw() <= len; i = svcntw()) {
svuint32_t input = svld1sb_u32(svptrue_b32(), (const int8_t *)s i);
svbool_t matches = svcmpne_n_u32(svptrue_b32(), input, 32);
svuint32_t compressed = svcompact_u32(matches, input);
svst1b_u32(svptrue_b32(), out8, compressed);
out8 = svcntp_b32(svptrue_b32(), matches);
}
if (i < len) {
svbool_t read_mask = svwhilelt_b32(i, len);
svuint32_t input = svld1sb_u32(read_mask, (const int8_t *)s i);
svbool_t matches = svcmpne_n_u32(read_mask, input, 32);
svuint32_t compressed = svcompact_u32(matches, input);
svst1b_u32(read_mask, out8, compressed);
out8 = svcntp_b32(read_mask, matches);
}
return out8 - reinterpret_cast<uint8_t *>(out);
}快个几倍大概
- Did you know that C 23 added support for formatting ranges?
int main() {
std::cout << std::format("{}", std::vector{1, 2, 3}); // [1, 2, 3]
std::cout << std::format("{:n}", std::vector{1, 2, 3}); // 1, 2, 3
std::cout << std::format("{}", std::tuple{'1', 2., 3}); // ('1', 2, 3)
std::cout << std::format("{}", std::vector{std::pair{'a',1}, std::pair{'b',2}}); // [(a, 1), (b, 2)]
std::cout << std::format("{:m}", std::vector{std::pair{'a',1}, std::pair{'b',2}}); // {(a, 1), (b, 2)}
}不多说
视频
- C Weekly - Ep 367 - Forgotten C : std::valarray
看到这里或许你有建议或者疑问或者指出错误，请留言评论! 多谢! 你的评论非常重要！
本文永久链接
如果有疑问评论最好在上面链接到评论区里评论
This site is open source. Improve this page.
