c/c++中动态内存分配处理字符串的细节问题

#include <stdio.h>

#include <stdlib.h>
#include <string.h>
#include <malloc.h>
 main()
{
  char *p;
  char *q;
  p=(char*)malloc(25*sizeof(char));
  if(p==NULL) exit(1);
  //q=(char*)malloc(10*sizeof(char));
  //if(q==NULL) exit(1);
 　strcpy(p,"dongbeijadlf");
  q="chenyudgf";
  printf("%s\n",q);
  printf("%s\n",p);
  strcat(p,q);
  printf("%s\n",p);
  free(p);
  p=NULL;
  //free(q);
  //q=NULL;
 }