C++ 如何在 C 中与 Linux 一起使用共享内存

有两种方法:shmget和mmap.我将谈论mmap，因为它更现代、更灵活，但如果你更愿意使用老式工具，可以看看man shmget(or this tutorial).

mmap()函数可用于分配具有高度可定制参数的内存缓冲区，以控制访问和权限，并在必要时为它们提供文件系统存储支持.

以下函数创建一个进程可以与其子进程共享的内存缓冲区:

#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>

void* create_shared_memory(size_t size) {
  // Our memory buffer will be readable and writable:
  int protection = PROT_READ | PROT_WRITE;

  // The buffer will be shared (meaning other processes can access it), but
  // anonymous (meaning third-party processes cannot obtain an address for it),
  // so only this process and its children will be able to use it:
  int visibility = MAP_SHARED | MAP_ANONYMOUS;

  // The remaining parameters to `mmap()` are not important for this use case,
  // but the manpage for `mmap` explains their purpose.
  return mmap(NULL, size, protection, visibility, -1, 0);
}

下面是一个示 routine 序，它使用上面定义的函数来分配缓冲区.父进程将编写一条消息fork，然后等待其子进程修改缓冲区.这两个进程都可以读取和写入共享内存.

#include <string.h>
#include <unistd.h>

int main() {
  char parent_message[] = "hello";  // parent process will write this message
  char child_message[] = "goodbye"; // child process will then write this one

  void* shmem = create_shared_memory(128);

  memcpy(shmem, parent_message, sizeof(parent_message));

  int pid = fork();

  if (pid == 0) {
    printf("Child read: %s\n", shmem);
    memcpy(shmem, child_message, sizeof(child_message));
    printf("Child wrote: %s\n", shmem);

  } else {
    printf("Parent read: %s\n", shmem);
    sleep(1);
    printf("After 1s, parent read: %s\n", shmem);
  }
}