解析char数据时出现分段错误(核心转储)

Question

我需要你的帮助.我有一个从端口读取gps和加速度计数据的程序.程序的工作方式如下:当我发送'a'时,prog会收到gps数据并发送到数据库,当我发送'b'时,prog会发送加速计数据并保存到数据库中.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计数据canot接收和错误是"分段错误.你能帮我解决问题吗？"

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;
}

---

谢谢您的帮助.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;

}

当我运行该程序时的结果是:

发送:INSERT INTO gps(纬度,经度)VALUES(-6.889760,107.619659)发送:b分段故障(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 (");

因为strcat()要求目标缓冲区在进入时以空值终止,并且它是未初始化的.这意味着strcat()将搜索query一个空字符,谁知道它将在哪里找到一个,可能超出其范围query将导致strcat()写入内存不应该.改成:

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

str稍后在代码中出现相同的错误.

而不是使用多个strcat()调用使用更安全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(来自第7.19.6.5节C99标准的snprintf函数):

snprintf函数返回已经写入的字符数已足够大,不计算终止空字符,如果发生编码错误则返回负值.因此,当且仅当返回值是非负且小于n时,才完全写入以null结尾的输出.