C language structure specifying initialization

Many times we don't use every member of the structure , Just want to initialize some of the members , At this time, you can use the specified initialization of the structure .

struct student {
    char *name;
    int num;
    int age;
    char group;
    float score;
} ;

（1） Under normal circumstances ： All variables must be initialized 
struct student stu1 ={"Tom",12,18,"A",136.5};

（2） Specified initialization ： Add a... Before the variable name “.”, Each line is separated by commas 
struct student stu1={
    .score=136.5,
    .age=18,
    .group="A",
} ;

example ：

struct test{
    int a;
    char b;
};
struct test c[] = {// Create three members , Partial initialization 
    [0] = {
        .a = 1,
    },
    [2] = {
        .b = 'a',
    },
};