Passing argc and argv to a thread in c

Question

Im trying to code a chat in C with a graphical interface. On one side, I have a client for my chat, on the other side I have a GTK app to display my chat. To run them both at the same time, I'll be using pthread (open to other suggestions tho).

My problem is that I need both argc and argv in order for my client to work properly. From what I saw, pthread_create() takes as argument a function to execute and only one argument. I saw from other topics that I could use a data structure to contain them both, but I can't seem to cast them properly. Here is what I have :

typedef struct {
    int *argc;
    char ** argv;
} args_list;

void * simple_client(void * arg){
    int argc = (int) arg->argc;
    char * argv[] = (char *) arg->argv;
    printf("in thread : %d / %s, %s \n", argc, argv[0], argv[1]);

    return 0;
}

int main(int argc, char * argv[])
{   
    printf("int main : %d / %s, %s \n", argc, argv[0], argv[1]);
    args_list * args = malloc(sizeof *args);
    args-> argc = &argc;
    args-> argv = &argv;

    pthread_t thread1;

    if (pthread_create(&thread1, NULL, simple_client, args)) {
        perror("pthread_create");
        return EXIT_FAILURE;
    }
    if (pthread_join(thread1, NULL)) {
        perror("pthread_join");
        return EXIT_FAILURE;
    }
    return EXIT_SUCCESS;
}

From this, I get : error: request for member 'argc' in something not a structure or union from int argc = (int) arg->argc; and the same with argv from char * argv[] = (char *) arg->argv;

What would be causing these errors ? And do you think this is a good way of implementating an online chat with a GTK gui ?

Thanks in advance

Answer 1

Define the struct as so:

typedef struct tARGS
{
    int argc;
    char **argv;
} ARGS;

Then, in main :

ARGS args;
args.argc = argc;
args.argv = argv;

Technically, argc isn't really needed since the following code will process every argument in args ( argv[argc] is a guaranteed null pointer by the C standard):

ARGS args = *(ARGS *)arg;
while(*args.argv)
{
    puts(*args.argv);
    args.argv++;
}

Answer 2

A few issues with types here.

simple_client takes a void* . In order to use the passed in value as an arg_list , you need to cast it to one.

void * simple_client(void * argp){
    arg_list* arg = (arg_list*) argp;

You don't need an extra level of indirection in arg_list . It should contain the same types as the arguments of main.

    //in main:
    args->argc = argc; 
    args->argv = argv; 

    //in simple_client:
    int argc =  arg->argc;
    char** argv = arg->argv;

In your original code you were storing the "address of a pointer to a char*" in a "pointer to a char *".