error: ‘class Stack’ has no member named ‘elem’

 #include <pthread.h>
class Stack{
public:
    Stack();
    ~Stack();
    int pop();
    void push(int);
private:
    static const int STACKSIZE;
    int elem[STACKSIZE];
    int top;
    pthread_mutex_t mutex;
    pthread_cond_t notfull, notempty;

};

#include "stack.h"
#include <pthread.h>
Stack::Stack():
        top(-1),
        mutex(PTHREAD_MUTEX_INITIALIZER),
        notfull(PTHREAD_COND_INITIALIZER),
        notempty(PTHREAD_COND_INITIALIZER)
{}

/*
same effect as
lock
while (isfull());
doit;
unlock
*/
const int Stack::STACKSIZE = 10;
void Stack::push(int v) {
    pthread_mutex_lock(&mutex);
    while (top == STACKSIZE) {//full?
        pthread_cond_wait(&notfull, &mutex);
    }
    this->elem[++top] = v;
    pthread_mutex_unlock(&mutex);
    pthread_cond_broadcast(&notempty);
}

int Stack::pop() {
    pthread_mutex_lock(&mutex);
    while (top == -1) {//empty?
        pthread_cond_wait(&notempty, &mutex);
    }
    int retval = elem[top--];
    pthread_mutex_unlock(&mutex);
    pthread_cond_broadcast(&notfull);
    return retval;
}

elem定义成public

没有对象可以直接用吗！！！！！，要么你改成static要么改成全局的。

对于STACKSIZE的定义，你这样写试一下
private:
static const int STACKSIZE=10;
int elem[STACKSIZE];
int top;
pthread_mutex_t mutex;
pthread_cond_t notfull, notempty;
再把后面定义的const int Stack::STACKSIZE = 10;注释掉