c - 不断获取垃圾值

Question

我正在开发一个程序，该程序从 USB 操纵杆获取轴值并通过 TCP 发送它。我所做的是首先让 TCP 程序工作，这样我就可以发送按预期工作的消息。然后我编写了另一个程序来从操纵杆获取值并将其打印到屏幕上，该程序也按预期工作。

我最近尝试的是将这两个独立的程序合并为一个，这样我就有一个服务器程序和一个客户端程序。这就是我的问题开始的地方，我在编译过程中没有收到任何错误。程序似乎不再从操纵杆获取值并将它们存储在变量 axis[0] 中。

现在我的流程是在连接了操纵杆的计算机上启动server.c 文件。然后我将在应该接收值的计算机上启动 client.c 文件。一路上我有几个 printf 语句来告诉我脚本到目前为止已经到达哪里。当我执行 server.c 脚本时，它告诉我检测到操纵杆并且有 6 个轴和 12 个按钮。然后它将循环等待，直到尝试来自客户端的连接。

执行client.c程序后，它将打印出The value is -1093458243。下面它将打印出来自 192.168.254.15 的传入连接 - 发送欢迎。然后客户端程序退出，这就是所发生的一切。

显示 The value is: 的行应该是 -32768 到 32767 之间的数字。因此它从某处获取了垃圾值。我迷路了，一整天都在尝试解决这个问题，但没有运气。我已经包含了几个代码示例，工作的 TCP server 和 client 脚本以及工作的 joystick 脚本以及我尝试将这两个脚本结合起来的代码和。任何人都可以发现我的代码中的任何错误，或者给我一些指示吗？

以下是 server.c 的组合代码:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>

//joysick libraries
#include <sys/ioctl.h>
#include <stdio.h>
#include <fcntl.h>
#include <linux/joystick.h>

//Joysick device
#define JOY_DEV "/dev/input/js0"

//TCP Port number
#define PORTNUM 2343

int main(int argc, char *argv[])
{

//TCP connect
    struct sockaddr_in dest; /* socket info about the machine connecting to us */
    struct sockaddr_in serv; /* socket info about our server */
    int mysocket;            /* socket used to listen for incoming connections */
    socklen_t socksize = sizeof(struct sockaddr_in);

    memset(&serv, 0, sizeof(serv));           /* zero the struct before filling the fields */
    serv.sin_family = AF_INET;                /* set the type of connection to TCP/IP */
    serv.sin_addr.s_addr = htonl(INADDR_ANY); /* set our address to any interface */
    serv.sin_port = htons(PORTNUM);           /* set the server port number */    

    mysocket = socket(AF_INET, SOCK_STREAM, 0);

    /* bind serv information to mysocket */
    bind(mysocket, (struct sockaddr *)&serv, sizeof(struct sockaddr));

    /* start listening, allowing a queue of up to 1 pending connection */
    listen(mysocket, 1);
    int consocket = accept(mysocket, (struct sockaddr *)&dest, &socksize);

//TCP variable
         char msg1[10];


//Joystick variables
        int xAxis;
    int yAxis;
        int xSpeed;
        int ySpeed;

//Joystick initialize
    int joy_fd, *axis=NULL, num_of_axis=0, num_of_buttons=0, x;
    char *button=NULL, name_of_joystick[80];
    struct js_event js;

    if( ( joy_fd = open( JOY_DEV , O_RDONLY)) == -1 )
    {
        printf( "Couldn't open joystick\n" );
        return -1;
    }

//Get number of axes, buttons and name of joystick. Print results to screen
        ioctl( joy_fd, JSIOCGAXES, &num_of_axis );
    ioctl( joy_fd, JSIOCGBUTTONS, &num_of_buttons );
    ioctl( joy_fd, JSIOCGNAME(80), &name_of_joystick );

    axis = (int *) calloc( num_of_axis, sizeof( int ) );
    button = (char *) calloc( num_of_buttons, sizeof( char ) );

    printf("Joystick detected: %s\n\t%d axis\n\t%d buttons\n\n"
        , name_of_joystick
        , num_of_axis
        , num_of_buttons );

//Use non blocking mode for joystick
    fcntl( joy_fd, F_SETFL, O_NONBLOCK );   /* use non-blocking mode */


    while(1) {
//Test to read joystick state
            /* read the joystick state */
        read(joy_fd, &js, sizeof(struct js_event));

            /* see what to do with the event */
        switch (js.type & ~JS_EVENT_INIT)
        {
            case JS_EVENT_AXIS:
                axis   [ js.number ] = js.value;
                break;
            case JS_EVENT_BUTTON:
                button [ js.number ] = js.value;
                break;
        }
//Give msg1 variable the value of axis[0]
    sprintf(msg1, "%d", axis[0]);

    //char msg1 = axis[0];
//TCP send
    while(consocket)
    {
    printf("Value is: %6d\n", axis[0]);
        printf("Incoming connection from %s - sending welcome\n", inet_ntoa(dest.sin_addr));
        send(consocket, msg1, strlen(msg1), 0); 
        consocket = accept(mysocket, (struct sockaddr *)&dest, &socksize);
    }

    close(consocket);
    close(mysocket);
    return EXIT_SUCCESS;

//Print joystick state to screen
    printf("Value is: %d", axis[0]);
    //printf(" \r");
    //fflush(stdout);   
    }


//Joystick close
    close( joy_fd );    /* too bad we never get here */
    return 0;

//TCP message
    //printf("Please enter info\n");
    //fgets(msg1, 20, stdin);

}

这是旧的工作 server.c 文件:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>

#define PORTNUM 2343

int main(int argc, char *argv[])
{
    char msg1[] = "Hello World !\n";

    struct sockaddr_in dest; /* socket info about the machine connecting to us */
    struct sockaddr_in serv; /* socket info about our server */
    int mysocket;            /* socket used to listen for incoming connections */
    socklen_t socksize = sizeof(struct sockaddr_in);

    memset(&serv, 0, sizeof(serv));           /* zero the struct before filling the fields */
    serv.sin_family = AF_INET;                /* set the type of connection to TCP/IP */
    serv.sin_addr.s_addr = htonl(INADDR_ANY); /* set our address to any interface */
    serv.sin_port = htons(PORTNUM);           /* set the server port number */    

    mysocket = socket(AF_INET, SOCK_STREAM, 0);

    /* bind serv information to mysocket */
    bind(mysocket, (struct sockaddr *)&serv, sizeof(struct sockaddr));

    /* start listening, allowing a queue of up to 1 pending connection */
    listen(mysocket, 1);
    int consocket = accept(mysocket, (struct sockaddr *)&dest, &socksize);

    while(consocket)
    {
        printf("Incoming connection from %s - sending welcome\n", inet_ntoa(dest.sin_addr));
        send(consocket, msg1, strlen(msg1), 0); 
        consocket = accept(mysocket, (struct sockaddr *)&dest, &socksize);
    }

    close(consocket);
    close(mysocket);
    return EXIT_SUCCESS;
}

这是client.c 文件:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>

#define MAXRCVLEN 500
#define PORTNUM 2343

int main(int argc, char *argv[])
{
   char buffer[MAXRCVLEN + 1]; /* +1 so we can add null terminator */
   int len, mysocket;
   struct sockaddr_in dest; 

   mysocket = socket(AF_INET, SOCK_STREAM, 0);

   memset(&dest, 0, sizeof(dest));                /* zero the struct */
   dest.sin_family = AF_INET;
   dest.sin_addr.s_addr = inet_addr("192.168.254.16"); /* set destination IP number */ 
   dest.sin_port = htons(PORTNUM);                /* set destination port number */

   connect(mysocket, (struct sockaddr *)&dest, sizeof(struct sockaddr));

   len = recv(mysocket, buffer, MAXRCVLEN, 0);

   /* We have to null terminate the received data ourselves */
   buffer[len] = '\0';

   printf("Received %s (%d bytes).\n", buffer, len);

   close(mysocket);
   return EXIT_SUCCESS;
}

这是获取值并将其打印到屏幕上的操纵杆文件:

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/joystick.h>
#include <wiringPi.h>
#define JOY_DEV "/dev/input/js0"

int main()
{
    int xAxis;
    int yAxis;
        int xSpeed;
        int ySpeed;

    FILE *fp;
        fp = fopen("/dev/servoblaster","w");
        if (fp == NULL) {
        printf("Error opening file");
        exit(0);
    }

    int joy_fd, *axis=NULL, num_of_axis=0, num_of_buttons=0, x;
    char *button=NULL, name_of_joystick[80];
    struct js_event js;

    if( ( joy_fd = open( JOY_DEV , O_RDONLY)) == -1 )
    {
        printf( "Couldn't open joystick\n" );
        return -1;
    }

    ioctl( joy_fd, JSIOCGAXES, &num_of_axis );
    ioctl( joy_fd, JSIOCGBUTTONS, &num_of_buttons );
    ioctl( joy_fd, JSIOCGNAME(80), &name_of_joystick );

    axis = (int *) calloc( num_of_axis, sizeof( int ) );
    button = (char *) calloc( num_of_buttons, sizeof( char ) );

    printf("Joystick detected: %s\n\t%d axis\n\t%d buttons\n\n"
        , name_of_joystick
        , num_of_axis
        , num_of_buttons );

    fcntl( joy_fd, F_SETFL, O_NONBLOCK );   /* use non-blocking mode */

    while( 1 )  /* infinite loop */
    {

            /* read the joystick state */
        read(joy_fd, &js, sizeof(struct js_event));

            /* see what to do with the event */
        switch (js.type & ~JS_EVENT_INIT)
        {
            case JS_EVENT_AXIS:
                axis   [ js.number ] = js.value;
                break;
            case JS_EVENT_BUTTON:
                button [ js.number ] = js.value;
                break;
        }

            /* print the results */

        //printf( "X: %6d  Y: %6d  ", axis[0], axis[1] );


        int xAxis = axis[0] / 327;
        int yAxis = axis[1] / 327;
        int ySpeed = 150-0.3*yAxis;
        int xSpeed = 150-0.3*xAxis;
        printf( "X is equal to: %d  Y is equal to: %d  Y speed is: %d ", xAxis, yAxis, ySpeed);

        fprintf(fp, "2=%d\n", ySpeed);
        fprintf(fp, "1=%d\n", xSpeed);
            printf("  \r");
        fflush(stdout);
    }

    close( joy_fd );    /* too bad we never get here */
    return 0;
}

Answer 1

对我来说有点奇怪(我认为这可能是你出现问题的原因)

fcntl( joy_fd, F_SETFL, O_NONBLOCK );   /* use non-blocking mode */

while( 1 )  /* infinite loop */
{

        /* read the joystick state */
    read(joy_fd, &js, sizeof(struct js_event));

您正在使用非阻塞模式，但没有检查read调用是否实际读取了任何内容。由于它是非阻塞的，即使操纵杆设备还没有可用的数据，它也会返回。