查询ipad可用内存

class MemoryTool {
public:
    static natural_t print_free_memory () {
        mach_port_t host_port;
        mach_msg_type_number_t host_size;
        vm_size_t pagesize;
       
        host_port = mach_host_self();
        host_size = sizeof(vm_statistics_data_t) / sizeof(integer_t);
        host_page_size(host_port, &pagesize);       
       
        vm_statistics_data_t vm_stat;
       
        if (host_statistics(host_port, HOST_VM_INFO, (host_info_t)&vm_stat, &host_size) != KERN_SUCCESS)
            NSLog(@"Failed to fetch vm statistics");
       
        /* Stats in bytes */
        natural_t mem_used = (vm_stat.active_count +
                              vm_stat.inactive_count +
                              vm_stat.wire_count) * pagesize;
        natural_t mem_free = vm_stat.free_count * pagesize;
        natural_t mem_total = mem_used + mem_free;
        NSLog(@"used: %u free: %u total: %u", mem_used, mem_free, mem_total);
        return mem_free;
    }
};