Question

我想将数据从用Matlab编写的客户端发送到用C编写的服务器。在读取服务器时，一次读取操作未接收到所有数据，并且将其分为两个连续的读取。

Matlab代码包含用于TCP服务器的代码，该TCP服务器接收一些数据，然后进行一些处理，然后通过TCP套接字作为客户端将处理的输出写入（发送）到C中的服务器。

这是用Matlab编写的客户端代码。

% A TCP server object defined for getting raw data and processing
% it. The object is called 'TCPServer'. It is not related to the 
% problem. 

% TCP client for sending the data to the C server
TCPClient = tcpip('192.168.1.2', 8080, 'NetworkRole', 'client');
set(TCPClient,'OutputBufferSize', 1464); 
% 1464 is total number of bytes of the struct to be sent
% to the C server.

set(TCPClient,'Timeout', 10);
fopen(TCPClient);

 while (1)
     while(1)       % Waits for incoming CSI data
         nBytes = get(TCPServer,'BytesAvailable');
         if nBytes >= bufferLen
             disp('Data received');
             break;
         end
     end

     data = fread(TCPServer,nBytes,'uint8');
     flushinput(TCPServer);

     % Does some processing and generate 'spec' and 'doas'
     % arrays to be sent to the C server

     message = [typecast(spec, 'uint8') typecast(doas, 'uint8')];
     fwrite(TCPClient, message); 
 end

这是用C语言编写的代码，用于服务器从Matlab中的客户端接收数据。

#define SA struct sockaddr

struct doa_struct {
    double spec[181], doa[2];
};

// Function that reads received data
void func(int sockfd) 
{ 
    struct doa_struct *doa_data;
    unsigned char buff[1464];
    int num_bytes;
    // infinite loop receiving data
    for (;;) { 
        bzero(buff, 1464); 

        // read the data from client and copy it in buffer 
        num_bytes = read(sockfd, buff, 1464);
        // Get the buffer which contains the client contents 
        doa_data = (struct doa_struct *) buff; 
        printf("doa: %f\t%f\t%d\n", doa_data->doa[0], doa_data->doa[1], num_bytes);
    }
} 

// Driver function 
int main()
{ 
    int sockfd, connfd, len;
    struct sockaddr_in servaddr, cli; 

    // socket create and verification
    sockfd = socket(AF_INET, SOCK_STREAM, 0); 
    if (sockfd == -1) { 
        printf("socket creation failed...\n"); 
        exit(0); 
    } 
    else
        printf("Socket successfully created..\n"); 
    bzero(&servaddr, sizeof(servaddr)); 

    // assign IP, PORT 
    servaddr.sin_family = AF_INET; 
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(8080); 

    // Binding newly created socket to given IP and verification
    if ((bind(sockfd, (SA*)&servaddr, sizeof(servaddr))) != 0) {
        printf("socket bind failed...\n");
        exit(0);
    }
    else
        printf("Socket successfully binded..\n");

    // Now server is ready to listen and verification
    if ((listen(sockfd, 5)) != 0) {
        printf("Listen failed...\n");
        exit(0);
    }
    else
        printf("Server listening..\n");
    len = sizeof(cli);

    // Accept the data packet from client and verification
    connfd = accept(sockfd, (SA*)&cli, &len);
    if (connfd < 0) {
        printf("server acccept failed...\n");
        exit(0); 
    } 
    else
        printf("server acccept the client...\n");

    // Function for chatting between client and server
    func(connfd);

    // After chatting close the socket
    close(sockfd); 
}

我在服务器上收到以下结果。

doa: 0.000000   0.000000    1408
doa: 0.000000   0.000000    56

每行打印都有三个值。前两个是接收的数据，不应为零。最后一个数字是服务器中read()函数接收的字节数。服务器在两行（两次read()操作）中接收到的字节总数为1464，这是客户端在一次fwrite()操作中发送的字节数。

正确的输出将是一行，如下所示：

doa: 25.000000  45.000000   1464

通过传输1464字节接收到的两个非零数据值。我还检查了客户端代码。客户端通过Matlab中的1464操作发送（写入）fwrite()字节。

Answer 1

read（）调用仅返回您期望的某些数据是完全正常的。发生这种情况的原因是，在较低级别上，网络堆栈将整个数据流分解为多个固定大小的数据包，以通过线路进行传输。在read（2）手册页中：

返回值...如果此数字小于请求的字节数，则不是错误；这个例如可能会发生，因为现在实际上实际可用的字节较少（也许因为我们接近文件末尾，或者因为我们正在从管道或文件中读取终端），或者因为read（）被信号中断。

在接收网络数据时，您需要继续调用read（），直到收到预期的字节数为止。例如，如下所示（未经测试的代码）：

void func(int sockfd) 
{ 
    struct doa_struct *doa_data;
    int expected_bytes = 1464;
    unsigned char buff[expected_bytes];
    int num_bytes;

    // Read a message
    bzero(buff, 1464);
    int bytes_read = 0;
    while (bytes_read < expected_bytes) {

        // read data into buff until we've read all the expected bytes
        // NOTE: if the Matlab side sends a malformed message, this could
        // hang in this loop forever...for real-world use, you'd need to
        // account for those types of scenarios.
        num_bytes = read(sockfd, buff + bytes_read, expected_bytes - bytes_read);
        if (num_bytes <= 0) {
            // handle error cases...
            return;
        }
        bytes_read += num_bytes;
    }

    // Get the buffer which contains the client contents 
    doa_data = (struct doa_struct *) buff; 
    printf("doa: %f\t%f\t%d\n", doa_data->doa[0], doa_data->doa[1], num_bytes);
}

关于您的输出为何打印0而不是预期值的原因：可能是因为您的printf格式说明符。您的编译器可能需要“％lf”来打印双精度字，而不是“％f”。传统上，双精度字符需要“％lf”，这是64位值而不是32位浮点值。但是，C99和更高版本的编译器可以使这一行模糊不清-参见this related stack overflow question。

Matlab中的客户端如何将二进制数据发送到C语言中的服务器？

1 个答案: