Thread: question about runtime error when deallocating pointer in struct

Simple question. I have a char pointer in a struct. When I try to free it, I get the following error at run time:

a.out(1186) malloc: *** error for object 0x1ffc: Non-aligned pointer being freed
*** set a breakpoint in malloc_error_break to debug

Why?

Code:

typedef struct foo {
  char *str;
} foo;

void
foo_free(foo *f) {
  free(f->str);
}

int
main(int argc, char **argv) {

  foo *f = malloc(sizeof(foo));
  f->str = "foo";
  foo_free(f);

  return 0;

}