【c】c pointer

double pointer

#include<stdio.h>
#include<stdlib.h>
int change_ptr(int** ptr);
int main()
{
  //int local =3;
  int *p =NULL;
  //*p = local;
  //printf("old *p =%d",p);
  printf("old p =%p\n",p);
  //printf("old  =%p",p);
  change_ptr(&p);
  printf("*p=%d\n",*p);
  printf("new p =%p\n",p);

  return 0;
}
int change_ptr (int **ptr)
{
  int *tmp = NULL;
  tmp = malloc(sizeof(int));
  *tmp = 4 ;
  *ptr = tmp ;
  return 0;
}

Makefile:

make:
	gcc -g  hello_rpms.c -o hello_rpms
clean:
	rm hello_rpms
install:
	mkdir -p ${DESTDIR}/usr/bin
	install -m 0755 hello_rpms ${DESTDIR}/usr/bin/hello_rpms