C Struct with char * str filed and fill struct array

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <uuid/uuid.h>

void retrieveUuid(char *uuidValue);

struct uuidStruct
{
    int id;
    char *str;
};

void array8();

int main()
{
    array8();
    return 0;
}

void retrieveUuid(char *uuidValue)
{
    uuid_t newUUID;
    uuid_generate(newUUID);
    uuid_unparse(newUUID,uuidValue);
}

void array8()
{
    struct uuidStruct arr[100];
    char *str=(char*)malloc(40);
    struct uuidStruct us; 
    
    for(int i=0;i<100;i++)
    {   
        us.str=(char*)malloc(40);
        retrieveUuid(str);          
        memcpy(us.str,str,strlen(str)); 
        us.id=i*i*i*i; 
        arr[i]=us;
    }

    for(int i=0;i<100;i++)
    {
        printf("Id=%d,str=%s\n",arr[i].id,arr[i].str);
        free(arr[i].str);
    }
    free(str);
}
 

Must be allocated memory via malloc before the struct instance initialization