CODEWITHSUNDEEP
cmultithreadingpthreads
Tomás Rodrigues
Tomás Rodrigues

Reputation: 544

How to pass multiples arguments to thread in c? [Segmentation fault]

I have tried to follow the procedures of several answers/tuturials and I'm still getting segmentation fault on passing multiple arguments to a thread? What am I doing wrong?

struct:

struct client_struct {
    int socketId;
    char *message;
};

process function:

// Handle socket session
void *process(void *client)
{
    client_struct *tmpClient = (client_struct*)client;
    char sendline[BUFFSIZE], recvline[BUFFSIZE];
    printf("can't reach this: %i\n", tmpClient->socketId);
    strncpy(sendline, tmpClient->message, sizeof(sendline)-1);
    sendline[sizeof(sendline)-1] = '\0';
}

called from main:

int sendMessage(const char *message, int sock)
{
    int result;
    pthread_t process_thread;

    struct client_struct * client;
    client->socketId = sock;
    strcpy(client->message, message);
    printf("segmentation fault here: %s\n", client->message);

    pthread_create(&process_thread, NULL, process, client);
    pthread_detach(process_thread);
}

Upvotes: 0

Views: 75

Answers (2)

Ilian Zapryanov
Ilian Zapryanov

Reputation: 1158

A simple proxyargs struct can be used also:

struct Args
{ int a; float f; char msg[10]; };
...
static void* callback(void* userData)
{
Args* a = (Args*) userData;
/* use args here */
}
...
Args mArgs = {10, 2.0, "message"};
pthread_create(&thread,NULL, callback, (Args*)&mArgs);
enter code here

Upvotes: 0

unalignedmemoryaccess
unalignedmemoryaccess

Reputation: 7441

Classic problem with undefined behavior when pointer is not initialized.

struct client_struct * client;

client = malloc(sizeof(*client)); //Allocate memory for client
client->... = ...; //DO you job

By doing struct client_struct * client; you are only declaring variable which will (probably at some point) point to data of type struct client_struct. Since you don't have your data yet, dereferencing non-initialized pointer leads to undefined behavior.

By using malloc, you are setting up valid data for your pointer.

Upvotes: 1

Related Questions