uart串口发送json格式的C程序

这是一个简单的示例程序，演示如何使用UART串口发送JSON格式的数据：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
#include <errno.h>
#include <json-c/json.h>

#define UART_DEVICE "/dev/ttyS0"
#define BAUDRATE B9600

int uart_fd;

int uart_init()
{
    struct termios tty;

    uart_fd = open(UART_DEVICE, O_RDWR | O_NOCTTY);
    if (uart_fd < 0) {
        perror("open");
        return -1;
    }

    memset(&tty, 0, sizeof(tty));
    if (tcgetattr(uart_fd, &tty) != 0) {
        perror("tcgetattr");
        return -1;
    }

    cfsetospeed(&tty, BAUDRATE);
    cfsetispeed(&tty, BAUDRATE);

    tty.c_cflag |= (CLOCAL | CREAD);
    tty.c_cflag &= ~CSIZE;
    tty.c_cflag |= CS8;
    tty.c_cflag &= ~PARENB;
    tty.c_cflag &= ~CSTOPB;
    tty.c_cflag &= ~CRTSCTS;

    tty.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
    tty.c_iflag &= ~(IXON | IXOFF | IXANY);
    tty.c_iflag &= ~INPCK;
    tty.c_iflag &= ~(ICRNL | IGNCR | INLCR);

    tty.c_oflag &= ~OPOST;

    tty.c_cc[VMIN] = 1;
    tty.c_cc[VTIME] = 0;

    if (tcsetattr(uart_fd, TCSANOW, &tty) != 0) {
        perror("tcsetattr");
        return -1;
    }

    return 0;
}

int uart_send_json(json_object *jobj)
{
    const char *json_str = json_object_to_json_string(jobj);
    int len = strlen(json_str);

    if (write(uart_fd, json_str, len) != len) {
        perror("write");
        return -1;
    }

    return 0;
}

int main()
{
    if (uart_init() != 0) {
        exit(EXIT_FAILURE);
    }

    json_object *jobj = json_object_new_object();
    json_object_object_add(jobj, "name", json_object_new_string("John"));
    json_object_object_add(jobj, "age", json_object_new_int(30));
    json_object_object_add(jobj, "height", json_object_new_double(1.75));
    json_object_object_add(jobj, "married", json_object_new_boolean(0));

    if (uart_send_json(jobj) != 0) {
        exit(EXIT_FAILURE);
    }

    json_object_put(jobj);
    close(uart_fd);

    exit(EXIT_SUCCESS);
}

这个程序首先使用`uart_init()`函数初始化UART串口，然后创建一个JSON对象`jobj`，将数据添加到其中，最后调用`uart_send_json()`函数将JSON字符串发送到串口。`uart_send_json()`函数将JSON对象转换为字符串，并使用`write()`函数将其发送到串口。发送完成后，程序释放JSON对象并关闭串口。