1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 | #include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <assert.h>
typedef struct {
int x;
int y;
} Point;
void set_point_to_zero_wrong(Point p) {
p.x = 0;
p.y = 0;
// WRONG because it operates on the copy of the 'Point' object that was passed as an argument.
}
void set_point_to_zero_correct(Point* a_p) {
a_p -> x = 0;
a_p -> y = 0;
// CORRECT because this modifies the object in the caller's stack frame.
}
int main(int argc, char* argv[]) {
Point p = { .x = 5, .y = 6 };
printf("BEFORE\n");
printf("p == { .x = %d, .y = %d }\n\n", p.x, p.y);
set_point_to_zero_wrong(p);
printf("AFTER set_point_to_zero_wrong(p)\n");
printf("p == { .x = %d, .y = %d }\n\n", p.x, p.y);
set_point_to_zero_correct(&p);
printf("AFTER set_point_to_zero_correct(&p)\n");
printf("p == { .x = %d, .y = %d }\n\n", p.x, p.y);
return EXIT_SUCCESS;
}
/* vim: set tabstop=4 shiftwidth=4 fileencoding=utf-8 noexpandtab: */
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