深入了解一下C语言中的柔性数组

struct S
{
int i;
int a[0];//柔性数组成员
}

struct S
{
int i;
int a[];//柔性数组成员
}

typedef struct S
{
	int i;
	char c[];//c是柔性数组
}S;

int main()
{
	S* p = (S*)malloc(sizeof(S) + 10 * sizeof(char));
	if (p == NULL)
	{
		perror("malloc");
		return 1;
	}
	p->i = 10;
	for (int i = 0; i < 10; i++)
	{
		p->c[i] = 'a';
	}
	free(p);
	p = NULL;
	return 0;
}

int main()
{
	S* p = (S*)malloc(sizeof(S) + 10 * sizeof(char));
	if (p == NULL)
	{
		perror("malloc");
		return 1;
	}
	p->i = 10;
	
	S* ptr = (S*)realloc(p, sizeof(S) + 20 * sizeof(char));
	if (ptr == NULL)
	{
		perror("realloc");
		return 1;
	}
	p = ptr;
	for (int i = 0; i < 20; i++)
	{
		p->c[i] = 'a';
	}

	free(p);
	p = NULL;
	return 0;
}

typedef struct S2
{
    it i;
    char* c;
}S2;

int main()
{
	S2* p = (S2*)malloc(sizeof(S2));
	p->i = 10;
	p->c = (char*)malloc(10 * sizeof(char));
	for (int i = 0; i < 10; i++)
	{
		p->c[i] = 'a';
	}

	free(p->c);
	p->c = NULL;
	free(p);
	p = NULL;

	return 0;
}