cout doesn't print string in C++ (include<iostream>, inlcude<string>, and flush all present) -

hi thank , let me try make simple :)

my code:
there array in class "table" hold newly added book (struct);
add put in 1 next 1 in array;
search can use isbn, title or author, variables in book (struct);
print supposed cout info of book

problem: print cant print string (variable in book string)

may not problem: insert,add...this kind of function should work because when search book, shows "book found"

#include<iostream> #include<string>  using namespace std;  struct book {     string isbn;     string title;     string author;     string date; }; class table { public:     //member constant     static const size_t capacity = 30;     //constructor     table() {used = 0;}     //modification     bool insert(book entry);     //constant     size_t hash_isbn(string target_isbn);     size_t hash_title(string target_title);     size_t hash_author(string target_author);     size_t search_isbn(string target_isbn);     size_t search_title(string target_title);     size_t search_author(string target_author);     void print(size_t index); private:     //member variables     book data[capacity];     size_t used; }; //modification member functions bool table::insert(book entry) {     if(search_isbn(entry.isbn))         return false;     data[used] = entry;     used++;     return true; } //constant member functions size_t table::hash_isbn(string target_isbn) {     size_t index = 0;     bool found = false;      while((index < used) && (!found))     {         if(data[index].isbn == target_isbn)         {             found = true;             continue;         }         index ++;     }     if(!found)         index = -1;     return index; } size_t table::hash_title(string target_title) {     size_t index = 0;     bool found = false;     while((index < used) && !found)     {         if(data[index].title == target_title)         {             found = true;             continue;         }         index ++;     }     if(index == used)         index = -1;     return index; } size_t table::hash_author(string target_author) {     size_t index = 0;     bool found = false;     while((index < used) && !found)     {         if(data[index].author == target_author)         {             found = true;             continue;         }         index ++;     }     if(index == used)         index = -1;     return index; } size_t table::search_isbn(string target_isbn) {     return hash_isbn(target_isbn)+1; } size_t table::search_title(string target_title) {     return hash_isbn(target_title)+1; } size_t table::search_author(string target_author) {     return hash_isbn(target_author)+1; } void table::print(size_t index) {     cout.flush();     cout<<data[index].title<<endl;     cout<<"title: "<<data[index].title<<endl;     cout<<"isbn: "<<data[index].isbn<<endl;     cout<<"author: "<<data[index].author<<endl;     cout<<"publication data: "<<data[index].date<<endl;     cout<<endl; } //nonmember functions void add(table t) {     book entry;     cout<<"enter author name:"<<endl;     cin>>entry.author;     cout<<endl;     cout<<"enter book name:"<<endl;     cin>>entry.title;     cout<<endl;     cout<<"enter isbn:"<<endl;     cin>>entry.isbn;     cout<<endl;     cout<<"enter publication data:"<<endl;     cin>>entry.date;     cout<<endl;      if(t.search_isbn(entry.isbn))         cout<<"==== book exists !!! ==="<<endl;///////////////////////输入重复时，此处并未执行     else         t.insert(entry); } void search(table t) {     string option;     cout<<"seach isbn (i), book title (t), or author (a). choice: ";     cin>>option;     cout<<endl;      while((option != "i") && (option != "t") && (option != "a"))     {         cout<<"not accessible option, try again:"<<endl             <<"seach isbn (i), book title (t), or author (a). choice: ";         cin>>option;         cout<<endl;     }      size_t index;      if(option == "i")     {         string target_isbn;         cout<<"enter isbn: ";         cin>>target_isbn;         cout<<endl;         index = t.search_isbn(target_isbn);     }     if(option == "t")     {         string target_title;         cout<<"enter title: ";         cin>>target_title;         cout<<endl;         index = t.search_isbn(target_title);     }     if(option == "a")     {         string target_author;         cout<<"enter author: ";         cin>>target_author;         cout<<endl;         index = t.search_isbn(target_author);     }       if(index+1)     {         cout<<"book found"<<endl;         t.print(index);     }     else         cout<<"==== book not exist !!! ==="<<endl; }  int main() {     table hash_table;     string action;     bool done = false;     while(!done)     {         cout<<"add new book (a), search (s), or end program (e)? ";         cin>>action;         cout<<endl;         while((action != "a") && (action != "s") && (action != "e"))         {             cout<<"not accessible option, try again:"<<endl                 <<"add new book (a), search (s), or end program (e)? ";             cin>>action;             cout<<endl;         }          if(action == "a")             add(hash_table);         if(action == "s")             search(hash_table);         if(action == "e")         {             done = true;             continue;         }     }      hash_table.print(0); // code try test problem in simple way       system("pause");     return 0; } 

the problem not print function or related it. in function add(and search too) pass table object value. pass reference.

void add(table& t) //            ^