CODEWITHSUNDEEP
unixstructpthreads
user975044
user975044

Reputation: 385

Pass struct to function through pthread

How do I pass a struct through the pthread_create to my function? The errors I keep getting are that lower and upper has not been defined which would lead me to believe that the struct was not passed properly. I have tried referencing lower as arg1.lower and my error back is saying im trying to request for the member of a non class type void*

void * mergeSortThread(void *arg1){
 std::ostringstream ostr;
 ostr << "begin: " << lower << " " << upper << endl;
 string message = ostr.str();
 write(2, message.data(), message.length());

}



int main(int argc, char** argv)
{

struct MergeSortThreadArg
{
int * array;
int * temp;
int lower, upper;

};

pthread_attr_t attr;
pthread_attr_init(&attr);
int arr[20];
int temp[20];

MergeSortThreadArg arg;
 arg.array = arr;
 arg.temp = temp;
 arg.lower = 0;
 arg.upper = 19;

pthread_create(th, &attr, mergeSortThread, &arg);
pthread_join(th[z], NULL);
return 0;
}

Upvotes: 0

Views: 204

Answers (1)

pmod
pmod

Reputation: 11007

Define struct before mergeSortThread() and add casting of arg1 to struct MergeSortThreadArg * it in mergeSortThread():

void * mergeSortThread(void *arg1){
   struct MergeSortThreadArg *p_MST = (struct MergeSortThreadArg *)arg1;
   std::ostringstream ostr;
   ostr << "begin: " << p_MST->lower << " " << p_MST->upper << endl;
   ...

Moreover, it's more correct/safe to allocate the struct and its fields (array and tmp) to avoid passing to new thread data located on stack of another thread.

Upvotes: 1

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