初始化结构体出现这个错误 error: C99 designator 'xx' outside aggregate initializer

#include <iostream>
using namespace std;

struct test{
    char charr[5];};

int main(){
    test t{
        .charr="ss"};

    cout<<" "<<t.charr<<endl;
    return 0;
}

//result
error: C99 designator 'charr' outside aggregate initializer        
         .charr="ss"};

 
#include <iostream>
#include <string.h>
using namespace std;
 
struct test{
    char charr[5];};
 
int main(){
    test t;
    strcpy(t.charr,"ss");
 
    cout<<" "<<t.charr<<endl;
    return 0;
}

供参考：

#include <iostream>
using namespace std;

struct test{
    char charr[5];};

int main(){
                  //test t{
                  //    .charr="ss"};
    struct test t = {"ss"};
    cout<<" "<<t.charr<<endl;
    system("pause");
    return 0;
}

但当我将charr填满又不会有错误了，这是为什么，像这样

//...
    test t{
        .charr="ssss"};
//...