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。在服务器中读取时，并非所有数据都是在一次读取操作中接收的，而是被分为两次连续读取。
Matlab代码包含TCP服务器的代码，该服务器接收一些数据，然后进行一些处理，然后通过TCP套接字将处理的输出作为客户端写入(发送(到C.中的服务器
以下是用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
以下是用C编写的代码，用于服务器在Matlab中接收来自客户端的数据。
#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: %ft%ft%dn", 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
打印的每一行都有三个值。前两个是接收到的不应为零的数据。最后一个数字是服务器中read()函数接收到的字节数。服务器在两行(两次read()操作(中接收的字节数之和为1464，即客户端在一次fwrite()操作中发送的字节数。
正确的输出应该是如下一行：
doa: 25.000000 45.000000 1464
通过1464字节的传输接收的两个非零数据值。我还检查了客户端代码。客户端在Matlab中通过fwrite()操作发送(写入(1464字节。
read((调用只返回您期望的一些数据是完全正常的。之所以会发生这种情况，是因为在较低级别，网络堆栈将整个数据流分解为多个固定大小的数据包，以便通过有线传输。阅读(2(手册页：
返回值。。。如果这个数字小于请求的字节数，则不是错误；这例如，可能会发生这种情况，因为现在实际可用的字节更少(可能因为我们接近文件末尾，或者因为我们正在从管道中读取，或者从终端(，或者因为read((被信号中断。
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。例如，类似这样的代码(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: %ft%ft%dn", doa_data->doa[0], doa_data->doa[1], num_bytes);
}
至于为什么您的输出打印0而不是预期值：这可能是因为您的printf格式说明符。编译器可能需要"%lf"来打印双精度，而不是"%f"。传统上，双精度需要"%lf"，双精度是64位值，而不是32位浮点值。然而，C99和更高版本的编译器可能会模糊这一行——请参阅这个相关的堆栈溢出问题。