C++ 中文周刊第13期

从reddit/hackernews/lobsters/meetingcpp摘抄一些c++动态。

每周更新

周刊项目地址 github，在线地址｜知乎专栏

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资讯

编译器信息最新动态推荐关注hellogcc公众号

本周周报github直达

zstd 1.5发布，性能提升巨大 https://github.com/facebook/zstd/releases/tag/v1.5.0

文章

Modules介绍
GCC 的整体架构

介绍了gcc的架构以及处理流程，值得一看，拓展眼界
tuple实现

介绍了tuple中的空基类优化

Practical Design Patterns: Opaque Pointers and Objects in C

看代码

Ringbuffer.h

#pragma once
  
#include <stdint.h>
#include <stdbool.h>
  
// Opaque pointer type to represent a ringbuffer instance
// 作者管这个叫opaque pointer
typedef struct ringbuffer_instance_t* ringbuffer_t;
  
// Functions that operate on an instance
ringbuffer_t ringbuffer_create(uint32_t capacity);
uint32_t ringbuffer_capacity(ringbuffer_t instance);
bool ringbuffer_enqueue(ringbuffer_t instance, uint8_t item);
bool ringbuffer_dequeue(ringbuffer_t instance, uint8_t* item);
void ringbuffer_destroy(ringbuffer_t instance);
  

ringbuffer.c

#include "ringbuffer.h"
#include <stdlib.h>
  
// Private struct, only accessible from within this file
struct ringbuffer_instance_t {
    volatile uint32_t wr_pos;
    volatile uint32_t rd_pos;
    uint8_t* data;
    uint32_t capacity;
};
  
ringbuffer_t ringbuffer_create(uint32_t capacity) {
    ringbuffer_t inst = calloc(1, sizeof(struct ringbuffer_instance_t));
    inst->data = calloc(capacity, sizeof(uint8_t));
    inst->capacity = capacity;
    inst->wr_pos = 0;
    inst->rd_pos = 0;
    return inst;
}
  
uint32_t ringbuffer_capacity(ringbuffer_t instance) {
    return instance->capacity;
}
  
bool ringbuffer_enqueue(ringbuffer_t instance, uint8_t item) {
    // implementation omitted
    return true;
}
  
bool ringbuffer_dequeue(ringbuffer_t instance, uint8_t* item) {
    // implementation omitted
    return true;
}
  
void ringbuffer_destroy(ringbuffer_t instance) {
    if (instance) {
        if (instance->data) {
            free(instance->data);
        }
        free(instance);
    }
}

作者管这个ringbuffer_t叫opaque pointer实际上就是一层不透明封装，当handle用。这个不是什么新的技巧了

暮无井见铃06-02 评论补充

Opaque pointer 就是 pImpl 的另一种习惯说法……其实很古老了，例如 C 标准都是允许 FILE 在头文件中仅声明不定义的。

Ambiguity in template parameters

讨论了一下模版NTTP和其他类型和concept一锅烩等场景，看个乐
Porting Intel Intrinsics to Arm Neon Intrinsics

手把手教你写sse移植代码(从x86到arm)
c++ tip of week 226 Did you know about C++23 feature which adds support for inheriting from std::variant?

std::variant支持继承，再实现operator()更方便std::visit 在线演示godbolt

struct value : std::variant<int, double> {
  using variant::variant;

  constexpr auto operator()(const auto& value) {
    std::clog << value << '\n';
  }
};

int main(){
  std::visit(value{}, std::variant<int, double>(42));  // prints 42
  std::visit(value{}, std::variant<int, double>(99.)); // prints 99
}