Gracias. Solucionado así :
#include <QtCore/QCoreApplication>
#include<stdio.h>
#include<vector>
using namespace std;
class primera
{
public:
int x;
};
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
primera pri;
primera *sec;
sec = &pri;
pri.x=1;
printf("%d\n",pri.x);
printf("%d\n",sec->x);
vector<primera> primus;
primus.resize(2);
primera* secus;
for(unsigned int i=0;i<primus.size();i++)
primus[i].x=2;
for(unsigned int i=0;i<primus.size();i++)
printf("%d\n", primus[i].x);
secus = &primus[0];
for(unsigned int i=0;i<primus.size();i++)
{
printf("%d\n", secus[i].x);
}
return a.exec();
}