c言語構造体の初期化のいくつかの方式

コンパイル環境:gcc version 5.4.020160609(Ubuntu 5.4.0-6 ubuntu 1~16.04.9)
テスト構造体宣言は次のとおりです.

struct person
{
  int age;
  char name[256];
}

1つ目:変数を定義し、[.]または[->]参照で初期化

// 
struct person p1;
p1.age = 20;
strcpy(p1.name, "xiaoming");
printf("age: %d
", p1.age);
printf("name: %s
", p1.name);

// 
struct person * p2 = NULL;
p2 = (struct person *)malloc(sizeof(*p2))
if(p2 != NULL)
{
  p2->age = 22;
  strcpy(p2->name, "xiaohong");
  printf("age: %d
", p2->age);
  printf("name: %s
", p2->name);
  free(p2);
  p2 = NULL;
}

2つ目:括弧に値を付けて初期化する

/** **/
// ,  
struct person p1 = {18, "xiaoming"};
printf("age: %d
", p1.age);
printf("name: %s
", p1.name);
// 
struct person p2;
p2 = (struct person){19, "xiaohong"};
printf("age: %d
", p2.age);
printf("name: %s
", p2.name);

/** **/
// ， 
struct person * p3 = NULL;
p3 = (struct person *)malloc(sizeof(*p3));
if(p3 != NULL)
{
  *p3 = (struct person){20, "xiaohua"}; 
  printf("age: %d
", p3->age);
  printf("name: %s
", p3->name);
  free(p3);
  p3 = NULL;
}

3つ目:カッコで[.]+[メンバー]linuxカーネルは、初期化順序に関係なく一般的に使用されます.繰り返しがある場合は、最後の初期化の値が有効になります.(ps:括弧の最後のカンマは加算可能か加算不可か)

/** **/
// 
struct person p1 = 
{
  .age = 20,
  .name = "xiaoming",
  .age = 21,
};
printf("age: %d
", p1.age);
printf("name: %s
", p1.name);
// 
struct person p2;
p2 = (struct person)
{
  .age = 21,
  .name = "xiaohong",
};
printf("age: %d
", p2.age);
printf("name: %s
", p2.name);

/** **/
// 
struct person * p3 = NULL;
p3 = (struct person *)malloc(sizeof(*p3));
if(p3 != NULL)
{
  *p3 = (struct person)
  {
    .age = 22,
    .name = "xiaohua",
  };
  printf("age: %d
", p3->age);
  printf("name: %s
", p3->name);
  free(p3);
  p3 = NULL;
}