c++ 共享内存demo

在C++中，共享内存是一种进程间通信（IPC）的技术，可以让多个进程直接访问同一块内存区域，而无需经过文件、网络或消息队列等中间环节。以下是一个简单的C++共享内存的demo示例，使用`boost::interprocess`库：

#include <boost/interprocess/shared_memory_object.hpp>
#include <boost/interprocess/mapped_region.hpp>
#include <cstdlib>
#include <cstring>

// 创建共享内存
int main() {
    // 锁定一个名字为"mySharedMemory"，大小为1MB的共享内存
    const char* sharedMemName = "mySharedMemory";
    const size_t memSize = 1024 * 1024; // 1MB
    std::error_code ec;
    boost::interprocess::shared_memory_object shm(boost::interprocess::open_or_create, sharedMemName, boost::interprocess::read_write);
    if (!shm.IsValid()) {
        throw std::runtime_error("Could not create shared memory");
    }
    shm.truncate(memSize); // 设置共享内存的大小

    // 创建映射区域，将共享内存映射到当前进程的地址空间
    boost::interprocess::mapped_region region(shm, boost::interprocess::read_write);
    void* ptr = region.get_address(); // 获取映射到的内存地址

    // 在映射区域写入数据
    std::memset(ptr, 'A', memSize);
    std::cout << "Wrote to shared memory.\n";

    // 在另一个进程中读取数据
    std::unique_ptr<boost::interprocess::shared_memory_object> shm2(
        new boost::interprocess::shared_memory_object(boost::interprocess::open_only, sharedMemName, boost::interprocess::read_only));
    boost::interprocess::mapped_region region2(shm2.get(), boost::interprocess::read_only);
    char* ptr2 = static_cast<char*>(region2.get_address());
    for (size_t i = 0; i < memSize; ++i) {
        if (ptr2[i] == 'A') {
            std::cout << "Read value at position " << i << ": A\n";
        } else {
            std::cout << "Read value at position " << i << ": Not A\n";
        }
    }

    // 关闭映射区域和共享内存
    region.close();
    shm.close();

    return 0;
}