在结构中分配内存时出现不可预知的行为

问：

我是 C 语言的新手，想知道内存分配和指针是如何工作的。但是我正在为我的代码的一些奇怪行为而苦苦挣扎。请参阅下面的代码和输出。我正在使用 mingw，gcc 版本 4.9.2 （tdm-1），不确定这是一个错误还是我遗漏了什么？这是向函数发送结构或从函数发送结构的正确方式吗？是否可以简单地将静态分配的数组分配给指针？顺便说一句，没有来自 gcc 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_s\n" );
  for ( int i = 0; i < 5; ++i ) {
    printf ( "%d\n", s.a [ i ] );
  }

  fill_s ( s );
  printf ( "\nfill_s\n" );
  for ( int i = 0; i < 5; ++i ) {
    printf ( "%d\n", s.a [ i ] );
  }

  copy_s_from_const ( s );
  printf ( "\ncopy_s_from_const\n" );
  for ( int i = 0; i < 5; ++i ) {
    printf ( "%d\n", s.a [ i ] );
  }

  kill_s ( s );

  // not working at all (array filled with garbage)
  fill1_s_from_const ( s );
  printf ( "\nfill1_s_from_const\n" );
  for ( int i = 0; i < 5; ++i ) {
    printf ( "%d\n", 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_const\n" );
  for ( int i = 0; i < 5; ++i ) {
    printf ( "%d\n", 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 ( "\ninline\n" );
  for ( int i = 0; i < 5; ++i ) {
    printf ( "%d\n", s.a [ i ] );
  }
}

输出