Passing structures in pthread - c

Question

I am trying to pass a structure when creating a thread but does not seem to work correctly!
Here is the structure:
struct analyse_data {
int verbose; //should be 1 or 0
};
Note that verbose can only be 1 or 0 and nothing else.
Here is the method being called (note it can be called multiple times by another method):
void dispatch(struct pcap_pkthdr *header, const unsigned char *packet,
int verbose) {
static bool thread_settings_initialised = false;
printf("Verbose: %d\n", verbose); //Prints 1 or 0
//Only run the first time dispatch method runs
if (thread_settings_initialised == false){
thread_settings_initialised = true;
//...
//Set mutex for the appropriate variables to remain thread safe
//...
//Set attr so threads are "Detached"
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
//Set pthread_cond_init
//...
}
//Put parameters into a struct so can be sent in a thread
struct analyse_data data;
data.verbose = verbose;
//...
pthread_t tid;
printf("data.verbose: %d\n", data.verbose); //This prints 1 or 0
int rc = pthread_create( &tid, &attr, bar, (void *) &data);
if (rc) {
printf("ERROR; return code from pthread_create() is %d\n", rc);
exit(-1);
}
}
and this is the method thats being called by the thread:
void analyse(void *thread_data) {
struct analyse_data *data;
data = (struct analyse_data *) thread_data;
int verbose = data->verbose;
printf("Verbose = %d\n", verbose ); //Prints weird numbers like -547845...
}
As you can see from my comments, the value of verbose changes when being used inside the method. Why? What am I doing Wrong?
Many Thanks!
Update (thanks to JS1)
I updated my code to use a pointer:
void dispatch(struct pcap_pkthdr *header, const unsigned char *packet,
int verbose) {
static bool thread_settings_initialised = false;
printf("Verbose: %d\n", verbose); //Prints 1 or 0
//...
//Put parameters into a struct so can be sent in a thread
struct analyse_data *data = malloc(sizeof(struct analyse_data)); //NEW
data->verbose = verbose;
//...
pthread_t tid;
printf("data.verbose: %d\n", data.verbose); //This prints 1 or 0
int rc = pthread_create( &tid, &attr, bar, (void *) data);
//...
}
But now the analyse() method always outputs 0, even when verbose is 1!

Answer 1

You should not pass a stack variable to pthread_create. Notice that data is local to the function dispatch and will be out of scope when dispatch returns. You should instead either use malloc to allocate data, or use a static or global variable.
If you use the malloc method, it will look like this:
struct analyse_data *data = malloc(sizeof(struct analyse_data));
data->verbose = verbose;
int rc = pthread_create( &tid, &attr, bar, data);
You must remember to not call free on data from dispatch. The memory should "belong" to the thread, so you should eventually call free on data from the thread when you are done using the contents of data.