在结构中分配内存时出现不可预测的行为

我是C语言的新手，想了解内存分配和指针是如何工作的。但我正在为我的代码的一些奇怪行为而挣扎。请参阅下面的代码和输出。我使用的是mingw，gcc 4.9.2版本(tdm-1(，不确定是错误还是我遗漏了什么？这是向函数发送结构的正确方式吗？简单地将静态分配的数组分配给指针可以吗？没有来自gcc btw.的警告

#include <stdlib.h>
#include <stdio.h>
typedef struct S {
int *a;
} s_t;
s_t
create_s () {
s_t s;
s.a = malloc ( sizeof ( int ) * 5 );
for ( int i = 0; i < 5; ++i ) {
s.a [ i ] = i << 1;
}
return s;
}
void
fill_s ( s_t s ) {
for ( int i = 0; i < 5; ++i ) {
s.a [ i ] = i;
}
}
void
kill_s ( s_t s ) {
free ( s.a );
}
void
fill1_s_from_const ( s_t s ) {
int array [ 5 ] = { 11, 21, 31, 41, 51 };
s.a = array;
}
s_t
fill2_s_from_const () {
int array [ 5 ] = { 12, 22, 32, 42, 52 };
s_t s;
s.a = array;
return s;
}
void
copy_s_from_const ( s_t s ) {
int array [ 5 ] = { 111, 222, 333, 444, 555 };
for ( int i = 0; i < 5; ++i ) {
s.a [ i ] = array [ i ];
}
}
int
main () {
s_t s = create_s ();
printf ( "ncreate_sn" );
for ( int i = 0; i < 5; ++i ) {
printf ( "%dn", s.a [ i ] );
}
fill_s ( s );
printf ( "nfill_sn" );
for ( int i = 0; i < 5; ++i ) {
printf ( "%dn", s.a [ i ] );
}
copy_s_from_const ( s );
printf ( "ncopy_s_from_constn" );
for ( int i = 0; i < 5; ++i ) {
printf ( "%dn", s.a [ i ] );
}
kill_s ( s );
// not working at all (array filled with garbage)
fill1_s_from_const ( s );
printf ( "nfill1_s_from_constn" );
for ( int i = 0; i < 5; ++i ) {
printf ( "%dn", s.a [ i ] );
}
// works partly (array filled correctly but some fields are still full of garbage)
s = fill2_s_from_const ();
printf ( "nfill2_s_from_constn" );
for ( int i = 0; i < 5; ++i ) {
printf ( "%dn", s.a [ i ] );
}
// same as fill1_s_from_const or fill2_s_from_const (imo) but works perfectly fine
int b [ 5 ] = { 11, 22, 33, 44, 55 };
s.a = b;
printf ( "ninlinen" );
for ( int i = 0; i < 5; ++i ) {
printf ( "%dn", s.a [ i ] );
}
}

输出