When compiling this program I receive an output that I would've never expected. When I reviewed this program I expected the outcome of pointer to be still "Hello, world!" because to my knowledge pointer was never affected by pointer2 . Yet, my output shows that when pointer is printed it contains pointer2 's string "y you guys!". How is this so?? Thanks!!
#include <stdio.h>
#include <string.h>
int main() {
char str_a[20];
char *pointer;
char *pointer2;
strcpy(str_a, "Hello, world!\n");
pointer = str_a;
printf(pointer);
pointer2 = pointer + 2;
printf(pointer2);
strcpy(pointer2, "y you guys!\n");
printf(pointer);
}
Output
Hello, world!
llo, world!
Hey you guys!
You have a single area of memory, the array str_a
.
After strcpy
call and the assignments to pointer
and pointer2
is looks something like this in memory:
+---+---+---+---+---+---+---+---+---+---+---+---+---+----+----+----------------------+ | H | e | l | l | o | , | | w | o | r | l | d | ! | \n | \0 | (uninitialized data) | +---+---+---+---+---+---+---+---+---+---+---+---+---+----+----+----------------------+ ^ ^ | | | pointer2 | pointer
The variable pointer
points to str_a[0]
and pointer2
points to str_a[2]
.
When you call strcpy
with pointer2
as the destination, you change the memory that pointer2
points to, which is the same array that pointer
also points to, just a couple of character further along.
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