Error with passing a pointer using threads - c++

Question

Updated code: 3/7/11 : 9:29pm
using namespace std;
void * matrixACreate(void * param);
void *status;
struct a
{
int Arow; // Matrix A
int Acol; // WxX
int low; // Range low
int high;
};
int main(int argc, char * argv[])
{
struct a matrix_mult_info;
matrix_mult_info.Arow = atoi(argv[1]); // Matrix A
matrix_mult_info.Acol = atoi(argv[2]); // WxX
matrix_mult_info.low = atoi(argv[5]); // Range low
matrix_mult_info.high = atoi(argv[6]);
pthread_t matrixAthread;
pthread_t runner;
int error, retValue;
struct a * a = (struct a *) malloc(sizeof(struct a));
error = pthread_create(&matrixAthread, NULL, matrixACreate, a );
//error = pthread_create(&matrixAthread, NULL, matrixBCreate, sendB);
retValue = pthread_join(matrixAthread, &status);
//retValue = pthread_join(matrixBthread, &status);
return 0;
}
void * matrixACreate(void * param) {
struct a * matrix = (struct a *) param;
int range = ((matrix->high - matrix->low) + 1);
cout << matrix->Arow << endl;
return 0;
}

Answer 1

struct a * a = (struct a *) malloc(sizeof(struct a));
// init a's members
error = pthread_create(&matrixAthread, NULL, matrixACreate, a);
EDIT: In response to updated question:
void * matrixACreate(void * param) {
struct a * matrix = (struct a *) param;
int range = ((matrix->high - matrix->low) + 1);
cout << matrix->Arow << endl;
return NULL;
}