#include <stdio.h>
int main(){
char *p, *initial;
int c, in=0;
for(initial=p; (c = getchar()) != EOF; p++, in++)
*p = c;
for(int i=0; i<in; i++)
printf("%p = %c\n", initial, *initial++);
}
For an input like hello hai, the program gives incomplete output:
0028FF29 = h
0028FF2A = e
0028FF2B = l
0028FF2C = l
0028FF2D =
0028FF2E =
0028FF2F =
0028FF30 =
0028FF31 =
It is working fine for small text, but it's not working for large text.
Undefined behavior. You don't set p to point to any valid memory location. So *p = c does not a well defined program make.
You can either have p point to a fixed sized buffer (if you know input will never be beyond a certain number of characters):
char buff[MAX_SIZE];
char *p = buff;
Or use dynamic memory allocation:
char *p = malloc(INITIAL_SIZE);
size_t current_size = INITIAL_SIZE;
// Later
if (p - initial == current_size) {
char *buff_new = realloc(initial, current_size * 2);
if (buff_new) {
initial = buff_new;
p = initial + current_size;
current_size *= 2;
}
else
// should probably abort here, the program is out of memory. Bad bad bad.
}
pis a pointer to an unallocated memory space .