Question

所以我在C中编写了一个app客户端服务器，客户端询问服务器的时间和服务器响应它。我正在使用struct。当我尝试从client.c中的服务器读取时出现分段错误。我在receiveTimeResponse上遇到分段错误，并试图找出原因。我认为它是因为我没有为char * date分配内存，但我想我做了。

结构：

struct timeStructQuer{
    int header[4];
    int requestID;
};

struct timeStructResponse{
    int header[4];
    int requestID;
    int length;
    char* date;
};

服务器：

int main()
{
    //connection here 
    struct queryStruct myStruct;
    read(client_sockfd, &myStruct, sizeof(myStruct));
    getCurrentTime(client_sockfd, myStruct);
}

void getCurrentTime(int client_sockfd, struct queryStruct str){
    int length;
    char* currentTime = malloc(sizeof(char) * 30);

    time_t rawtime;
    struct tm * timeinfo;
    time (&rawtime);
    timeinfo = localtime (&rawtime);
    length = sprintf (currentTime ,"%s", asctime (timeinfo));

    struct timeStructResponse response;
    response.date = malloc(sizeof(char) * length);
    response.header[0] = 1;
    response.header[1] = 0;
    response.header[2] = 0;
    response.header[3] = 2;
    response.requestID = str.requestID;
    response.length = length;
    response.date = currentTime;

    write(client_sockfd, &response, sizeof(response));
}

客户端：

int main()
{
    //connection here
    sendTimeQuery(sockfd);
    receiveTimeResponse(sockfd);

    exit(0);
}

void sendTimeQuery(int sockfd){

    struct queryStruct myStruct;

    int randomN = rand();
    myStruct.header[0] = 0;
    myStruct.header[1] = 0;
    myStruct.header[2] = 0;
    myStruct.header[3] = 2;
    myStruct.requestID = randomN;

    write(sockfd, &myStruct, sizeof(myStruct));
}

void receiveTimeResponse(int sockfd){       
    struct timeStructResponse response;
    response.date = malloc(sizeof(char) * 30);
    printf("seg2");
    read(sockfd, &response, sizeof(response));
    printf("Current time: %s", response.date);
}

Answer 1

read(sockfd, &response, sizeof(response));将使用无效值覆盖先前已分配的response.data指针。问题是你不能传递指针（实际上你可以，但指针值在另一侧无效）。您需要传输他们指向的数据。所以写应该是这样的：

/* TODO check write results... */
write(client_sockfd, &response.header, sizeof(response.header));
write(client_sockfd, &response.requestID, sizeof(response.requestID));
write(client_sockfd, &response.length, sizeof(response.length));
write(client_sockfd, response.date, response.length);

并且如下所示：

/* TODO check read and malloc results, length, and date is properly null-terminated... */
read(sockfd, &response.header, sizeof(response.header));
read(sockfd, &response.requestID, sizeof(response.requestID));
read(sockfd, &response.length, sizeof(response.length));
response.date = (char *) malloc(response.length);
read(sockfd, response.date, response.length);

使用套接字读取char *时出现分段错误

1 个答案: