c - 解析char数据时出现Segmentation fault (core dumped)

Question

我需要你的帮助。我有一个程序可以从端口读取 gps 和加速度计数据。程序是这样工作的:当我发送“a”时，程序将接收 gps 数据并发送到数据库，当我发送“b”时，程序将发送加速度计数据并保存到数据库。但是当我运行程序时，gps 数据成功接收并发送到数据库，但加速度计数据无法接收，错误是“段错误”。你能帮我解决这个问题吗..？

int main(void) {

    int fd;
    fd = open("/dev/ttyACM0", O_RDWR | O_NOCTTY | O_NDELAY);
    if (fd == -1) {
        perror("open_port: Unable to open port ");
    } else {
        fcntl(fd, F_SETFL, 0);
    }

    char a[] = "a";
    char b[] = "b";

    int n,m,cnt;
    char in[30];
    //char in2[50];
    //char *in;
    //char in2[100];
    //in = (char*) malloc(i+1);
    //if (in == NULL) exit(1);


    MYSQL *conn;

    const char *localhost   = "127.0.0.1";
    const char *user     = "root";
    const char *password = "";
    const char *database = "arduino1";

    conn = mysql_init(NULL);

    // Connect to database 
    if (!mysql_real_connect(conn, localhost, user, password, database, 0, NULL, 0))
    {
          fprintf(stderr, "%s\n", mysql_error(conn));
          exit(1);
    } 


    for(cnt=0; cnt<5; cnt++) 
    {
        if (cnt < 1) {
            sleep(2);
            n = write(fd, a, sizeof(a));
            printf("Send : %s \n", a);

            //terima data gps dari port
            sleep(1);
            n = read(fd, in, 100);
            if (n < 0)
            {
                perror("read");
                break;
            }

            //query gps         
            char c_lat[50],c_lon[50];
            tokenizer(in,c_lat,c_lon);


            //Isi nilai gps ke database

            char query[255];

            strcat(query,"INSERT INTO gps (latitude, longitude) VALUES (");
                strcat(query,c_lat);
                strcat(query,",");
                strcat(query,c_lon);
                strcat(query,")");

            if (mysql_query(conn, query));
            {
              printf("%s\n", query);
            }


     } else {
            m = write(fd, b, sizeof(b));
            printf("Send : %s \n", b);

            //terima data accelerometer dari port
            sleep(1);
            m = read(fd, in, 100);

            in[m] = '\0';   

            char str[255];

            //query accelerometer   
            char c_nilai_x[10],c_nilai_y[10],c_nilai_z[10],c_teg[6];
            tokenizer_acm(in,c_nilai_x,c_nilai_y,c_nilai_z,c_teg);


            //Isi nilai accelerometer ke database



            strcat(str,"INSERT INTO highcharts_php (x_axis, y_axis, z_axis, tegangan) VALUES (");
                strcat(str,c_nilai_x);
                strcat(str,",");
                strcat(str,c_nilai_y);
                strcat(str,",");
                strcat(str,c_nilai_z);
                strcat(str,",");
                strcat(str,c_teg);
                strcat(str,")");

            if (mysql_query(conn, str));
            {
              printf("%s\n", str);
            }

        }


        // Close database connection
        mysql_close(conn);

    }

    return 0;
}

---

感谢您的帮助。但我仍然收到同样的错误。我的改变是这样的:int main(void) {

int fd;
fd = open("/dev/ttyACM0", O_RDWR | O_NOCTTY | O_NDELAY);
if (fd == -1) {
    perror("open_port: Unable to open port ");
} else {
    fcntl(fd, F_SETFL, 0);
}

char a[] = "a";
char b[] = "b";

int n,m,cnt;
char in[50];

MYSQL *conn;

const char *localhost   = "127.0.0.1";
const char *user     = "root";
const char *password = "";
const char *database = "arduino1";

conn = mysql_init(NULL);

// Connect to database 
if (!mysql_real_connect(conn, localhost, user, password, database, 0, NULL, 0))
{
      fprintf(stderr, "%s\n", mysql_error(conn));
      exit(1);
} 


for(cnt=0; cnt<5; cnt++) 
{
    if (cnt < 1) {
        sleep(2);
        n = write(fd, a, sizeof(a));
        printf("Send : %s \n", a);

        //terima data gps dari port
        sleep(1);
        n = read(fd, in, 20);
        if (n < 0)
        {
            perror("read");
            break;
        }

        //query gps         
        char c_lat[10],c_lon[9];
        tokenizer(in,c_lat,c_lon);


        //Isi nilai gps ke database

        char query[255] = "INSERT INTO gps (latitude, longitude) VALUES (";
            strcat(query,c_lat);
            strcat(query,",");
            strcat(query,c_lon);
            strcat(query,")");

        if (mysql_query(conn, query));
        {
          printf("%s\n", query);
        }


 } else {
        m = write(fd, b, sizeof(b));
        printf("Send : %s \n", b);

        //terima data accelerometer dari port
        sleep(1);
        m = read(fd, in, 30);

        in[m] = '\0';   



        //query accelerometer   
        char c_nilai_x[8],c_nilai_y[8],c_nilai_z[8],c_teg[4];
        tokenizer_acm(in,c_nilai_x,c_nilai_y,c_nilai_z,c_teg);


        //Isi nilai accelerometer ke database


        char str[255] = "INSERT INTO highcharts_php (x_axis, y_axis, z_axis, tegangan) VALUES (";
            strcat(str,c_nilai_x);
            strcat(str,",");
            strcat(str,c_nilai_y);
            strcat(str,",");
            strcat(str,c_nilai_z);
            strcat(str,",");
            strcat(str,c_teg);
            strcat(str,")");

        if (mysql_query(conn, str));
        {
          printf("%s\n", str);
        }

    }


    // Close database connection
    mysql_close(conn);

}

return 0;

我运行程序的结果是:

发送:一个插入 gps(纬度、经度)值(-6.889760,107.619659)发送:b段错误(核心转储)

我需要帮助....谢谢

Answer 1

这是一个错误:

char query[255];
strcat(query,"INSERT INTO gps (latitude, longitude) VALUES (");

作为strcat()要求目标缓冲区在进入时为 null 终止，并且未初始化。这意味着 strcat() 将在 query 中搜索一个空字符，谁知道它会在哪里找到一个空字符，可能超出了 query 的范围这将导致 strcat() 写入不应该的内存。更改为:

char query[255] = "INSERT INTO gps (latitude, longitude) VALUES (";

代码后面的 str 也有同样的错误。

不要使用多个 strcat() 调用，而是使用更安全的 snprintf() :

char query[255];
int result = snprintf(query,
                      255,
                      "INSERT INTO gps (latitude, longitude) VALUES (%s,%s)",
                      c_lat,
                      c_lon);

/* See following paragraph for explanation of this condition. */
if (result > 0 && result < 255)
{
}

snprintf() 返回值(来自 C99 标准的 7.19.6.5 The snprintf function 部分):

The snprintf function returns the number of characters that would have been written had n been sufficiently large, not counting the terminating null character, or a negative value if an encoding error occurred. Thus, the null- terminated output has been completely written if and only if the returned value is nonnegative and less than n.