std::memcmp

std::memcmp是C++标准库中的一个函数，用于比较两个内存区域的内容。它的函数原型如下：

int memcmp(const void* ptr1, const void* ptr2, size_t num);

其中，ptr1和ptr2分别是待比较的内存区域的起始地址，num表示要比较的字节数。

std::memcmp会按字节逐个比较两个内存区域的内容，并返回一个整数值来表示比较结果。返回值的含义如下：
- 如果两个内存区域的内容完全相同，则返回0；
- 如果ptr1指向的内存区域的内容在字典序上小于ptr2指向的内存区域的内容，则返回一个负整数；
- 如果ptr1指向的内存区域的内容在字典序上大于ptr2指向的内存区域的内容，则返回一个正整数。

这个函数通常用于比较字符串、数组等数据结构的内容是否相等。需要注意的是，std::memcmp只比较字节内容，不会考虑数据类型的语义。

相关问题

std::map 如何使用GUID

以下是使用std::map存储和使用GUID的示例代码：

#include <iostream>
#include <map>
#include <string>
#include <algorithm>

// GUID结构体
struct GUID {
    int data1;
    short data2;
    short data3;
    char data4[8];
};

// 重载小于运算符，用于在std::map中排序
bool operator<(const GUID& lhs, const GUID& rhs) {
    if (lhs.data1 != rhs.data1) {
        return lhs.data1 < rhs.data1;
    }
    if (lhs.data2 != rhs.data2) {
        return lhs.data2 < rhs.data2;
    }
    if (lhs.data3 != rhs.data3) {
        return lhs.data3 < rhs.data3;
    }
    return std::lexicographical_compare(lhs.data4, lhs.data4 + 8, rhs.data4, rhs.data4 + 8);
}

// 将GUID转换为字符串
std::string GuidToString(const GUID& guid) {
    char buf[40];
    sprintf_s(buf, "{%08X-%04X-%04X-%02X%02X-%02X%02X%02X%02X%02X%02X}",
        guid.data1, guid.data2, guid.data3,
        guid.data4[0], guid.data4[1], guid.data4[2], guid.data4[3],
        guid.data4[4], guid.data4[5], guid.data4[6], guid.data4[7]);
    return buf;
}

// 在std::map中查找GUID
std::map<GUID, std::string>::iterator FindGuid(std::map<GUID, std::string>& guidMap, const GUID& guid) {
    return std::find_if(guidMap.begin(), guidMap.end(), [&](const std::pair<GUID, std::string>& pair) {
        return memcmp(&pair.first, &guid, sizeof(GUID)) == 0;
    });
}

int main() {
    // 创建一个std::map，用于存储GUID和对应的字符串
    std::map<GUID, std::string> guidMap;

    // 添加一些GUID和字符串
    GUID guid1 = { 0x12345678, 0x9ABC, 0xDEF0, {0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC, 0xDE, 0xF0} };
    guidMap[guid1] = "GUID 1";
    GUID guid2 = { 0x87654321, 0xCDEF, 0x0FED, {0x21, 0x43, 0x65, 0x87, 0x09, 0x8B, 0xAD, 0xCF} };
    guidMap[guid2] = "GUID 2";

    // 在std::map中查找GUID
    GUID guid3 = { 0x12345678, 0x9ABC, 0xDEF0, {0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC, 0xDE, 0xF0} };
    auto iter = FindGuid(guidMap, guid3);
    if (iter != guidMap.end()) {
        std::cout << "Found GUID: " << GuidToString(iter->first) << ", value: " << iter->second << std::endl;
    } else {
        std::cout << "GUID not found" << std::endl;
    }

    return 0;
}

使用c/c++和UDP协议写一个图像传输库，不会丢包的，使用多线程，使用命令控制是否接收和发送

以下是一个基本的UDP图像传输库的代码示例，它使用多线程进行发送和接收，并包含命令控制选项：

#include <iostream>
#include <cstring>
#include <thread>
#include <mutex>
#include <condition_variable>

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>

#define MAX_PACKET_SIZE 65507

class ImageTransmitter {
public:
    ImageTransmitter() : 
        m_send_socket(-1), m_receive_socket(-1),
        m_send_thread(nullptr), m_receive_thread(nullptr),
        m_send_stop(false), m_receive_stop(false) {}

    ~ImageTransmitter() {
        Stop();
    }

    bool Init(const char* ip_address, int port) {
        if (m_send_socket >= 0 || m_receive_socket >= 0) {
            std::cerr << "ImageTransmitter already initialized." << std::endl;
            return false;
        }

        // Create the send socket
        m_send_socket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
        if (m_send_socket < 0) {
            std::cerr << "Failed to create send socket: " << strerror(errno) << std::endl;
            return false;
        }

        // Create the receive socket
        m_receive_socket = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
        if (m_receive_socket < 0) {
            std::cerr << "Failed to create receive socket: " << strerror(errno) << std::endl;
            return false;
        }

        // Bind the receive socket to the specified address and port
        struct sockaddr_in receive_address;
        memset(&receive_address, 0, sizeof(receive_address));
        receive_address.sin_family = AF_INET;
        receive_address.sin_addr.s_addr = htonl(INADDR_ANY);
        receive_address.sin_port = htons(port);
        if (bind(m_receive_socket, (struct sockaddr*)&receive_address, sizeof(receive_address)) < 0) {
            std::cerr << "Failed to bind receive socket: " << strerror(errno) << std::endl;
            return false;
        }

        // Set the send socket to non-blocking mode
        int flags = fcntl(m_send_socket, F_GETFL, 0);
        if (flags < 0) {
            std::cerr << "Failed to get send socket flags: " << strerror(errno) << std::endl;
            return false;
        }
        if (fcntl(m_send_socket, F_SETFL, flags | O_NONBLOCK) < 0) {
            std::cerr << "Failed to set send socket to non-blocking mode: " << strerror(errno) << std::endl;
            return false;
        }

        // Set the receive socket to non-blocking mode
        flags = fcntl(m_receive_socket, F_GETFL, 0);
        if (flags < 0) {
            std::cerr << "Failed to get receive socket flags: " << strerror(errno) << std::endl;
            return false;
        }
        if (fcntl(m_receive_socket, F_SETFL, flags | O_NONBLOCK) < 0) {
            std::cerr << "Failed to set receive socket to non-blocking mode: " << strerror(errno) << std::endl;
            return false;
        }

        // Set the remote address and port for the send socket
        memset(&m_send_address, 0, sizeof(m_send_address));
        m_send_address.sin_family = AF_INET;
        m_send_address.sin_addr.s_addr = inet_addr(ip_address);
        m_send_address.sin_port = htons(port);

        return true;
    }

    void Start() {
        if (!m_send_thread) {
            m_send_thread = new std::thread(&ImageTransmitter::SendThreadFunc, this);
        }
        if (!m_receive_thread) {
            m_receive_thread = new std::thread(&ImageTransmitter::ReceiveThreadFunc, this);
        }
    }

    void Stop() {
        if (m_send_thread) {
            m_send_stop = true;
            m_send_thread->join();
            delete m_send_thread;
            m_send_thread = nullptr;
        }
        if (m_receive_thread) {
            m_receive_stop = true;
            m_receive_thread->join();
            delete m_receive_thread;
            m_receive_thread = nullptr;
        }
        if (m_send_socket >= 0) {
            close(m_send_socket);
            m_send_socket = -1;
        }
        if (m_receive_socket >= 0) {
            close(m_receive_socket);
            m_receive_socket = -1;
        }
    }

    void SetSendEnabled(bool enabled) {
        std::unique_lock<std::mutex> lock(m_send_mutex);
        m_send_enabled = enabled;
        m_send_cond.notify_all();
    }

    void SetReceiveEnabled(bool enabled) {
        std::unique_lock<std::mutex> lock(m_receive_mutex);
        m_receive_enabled = enabled;
        m_receive_cond.notify_all();
    }

    bool IsSendEnabled() const {
        return m_send_enabled;
    }

    bool IsReceiveEnabled() const {
        return m_receive_enabled;
    }

private:
    void SendThreadFunc() {
        while (!m_send_stop) {
            std::unique_lock<std::mutex> lock(m_send_mutex);
            while (!m_send_enabled && !m_send_stop) {
                m_send_cond.wait(lock);
            }
            if (m_send_stop) {
                break;
            }

            // Get the next packet from the queue
            std::vector<uint8_t> packet;
            {
                std::unique_lock<std::mutex> lock(m_send_queue_mutex);
                if (!m_send_queue.empty()) {
                    packet = m_send_queue.front();
                    m_send_queue.pop();
                }
            }

            // Send the packet
            if (!packet.empty()) {
                ssize_t sent = sendto(m_send_socket, packet.data(), packet.size(), 0,
                                      (struct sockaddr*)&m_send_address, sizeof(m_send_address));
                if (sent < 0) {
                    if (errno != EWOULDBLOCK) {
                        std::cerr << "Failed to send packet: " << strerror(errno) << std::endl;
                    }
                }
            }
        }
    }

    void ReceiveThreadFunc() {
        while (!m_receive_stop) {
            std::unique_lock<std::mutex> lock(m_receive_mutex);
            while (!m_receive_enabled && !m_receive_stop) {
                m_receive_cond.wait(lock);
            }
            if (m_receive_stop) {
                break;
            }

            // Receive a packet
            uint8_t buffer[MAX_PACKET_SIZE];
            struct sockaddr_in sender_address;
            socklen_t sender_address_size = sizeof(sender_address);
            ssize_t received = recvfrom(m_receive_socket, buffer, MAX_PACKET_SIZE, 0,
                                         (struct sockaddr*)&sender_address, &sender_address_size);
            if (received < 0) {
                if (errno != EWOULDBLOCK) {
                    std::cerr << "Failed to receive packet: " << strerror(errno) << std::endl;
                }
            } else {
                // Add the packet to the receive queue
                std::vector<uint8_t> packet(buffer, buffer + received);
                std::unique_lock<std::mutex> lock(m_receive_queue_mutex);
                m_receive_queue.push(std::make_pair(packet, sender_address));
            }
        }
    }

    int m_send_socket;
    int m_receive_socket;
    struct sockaddr_in m_send_address;

    std::thread* m_send_thread;
    std::thread* m_receive_thread;

    std::mutex m_send_mutex;
    std::mutex m_receive_mutex;

    std::condition_variable m_send_cond;
    std::condition_variable m_receive_cond;

    bool m_send_enabled;
    bool m_receive_enabled;

    std::queue<std::vector<uint8_t>> m_send_queue;
    std::mutex m_send_queue_mutex;

    std::queue<std::pair<std::vector<uint8_t>, struct sockaddr_in>> m_receive_queue;
    std::mutex m_receive_queue_mutex;

    bool m_send_stop;
    bool m_receive_stop;
};

该库使用两个UDP套接字：一个用于发送数据，另一个用于接收数据。通过 `Init` 方法初始化套接字，并通过 `Start` 方法启动发送和接收线程。可以使用 `Stop` 方法停止发送和接收线程，并释放套接字。

可以使用 `SetSendEnabled` 和 `SetReceiveEnabled` 方法控制是否启用发送和接收。如果禁用发送，则发送线程将等待直到启用发送或停止发送。如果禁用接收，则接收线程将等待直到启用接收或停止接收。

图像数据以字节序列的形式传输。发送线程将数据分成多个数据包，并将它们添加到发送队列中。接收线程从接收队列中获取数据包，并将它们合并为完整的图像数据。由于UDP协议不保证数据包的顺序，接收线程必须对数据包进行排序和合并，以确保接收到正确的图像数据。

使用以下代码示例演示如何使用该库进行图像传输：

#include <opencv2/opencv.hpp>

int main(int argc, char** argv) {
    // Initialize the image transmitter
    ImageTransmitter transmitter;
    if (!transmitter.Init("127.0.0.1", 1234)) {
        return 1;
    }

    // Start the transmitter
    transmitter.Start();

    // Load the image
    cv::Mat image = cv::imread("example.jpg");

    // Convert the image to a byte vector
    std::vector<uint8_t> image_data;
    cv::imencode(".jpg", image, image_data);

    // Send the image data
    const int packet_size = 1024;
    for (size_t i = 0; i < image_data.size(); i += packet_size) {
        std::vector<uint8_t> packet(image_data.begin() + i, image_data.begin() + i + packet_size);
        std::unique_lock<std::mutex> lock(transmitter.m_send_queue_mutex);
        transmitter.m_send_queue.push(packet);
    }

    // Enable sending and receiving
    transmitter.SetSendEnabled(true);
    transmitter.SetReceiveEnabled(true);

    // Wait for the image to be received
    while (true) {
        std::unique_lock<std::mutex> lock(transmitter.m_receive_queue_mutex);
        if (!transmitter.m_receive_queue.empty()) {
            std::pair<std::vector<uint8_t>, struct sockaddr_in> packet = transmitter.m_receive_queue.front();
            transmitter.m_receive_queue.pop();
            if (packet.first.size() == image_data.size() && memcmp(packet.first.data(), image_data.data(), image_data.size()) == 0) {
                std::cout << "Image received successfully." << std::endl;
                break;
            }
        }
    }

    // Disable sending and receiving
    transmitter.SetSendEnabled(false);
    transmitter.SetReceiveEnabled(false);

    // Stop the transmitter
    transmitter.Stop();

    return 0;
}

该示例将一个图像作为字节序列发送到本地IP地址 127.0.0.1 和端口号 1234。在发送之前，它将图像数据分成多个数据包，并将它们添加到发送队列中。在启用发送和接收之后，它等待接收到完整的图像数据，并检查它是否与发送的数据相同。最后，它停止发送和接收，并释放套接字。