CODEWITHSUNDEEP
c++stl
Pranav Bhatia
Pranav Bhatia

Reputation: 540

Iterating map in C++ containing class objects

I am creating a map in C++ which contains a integer key and the value is an object of class User. I am able to insert the object into the map with the following code - 

std::map<std::string,User>::iterator it = usermap.begin();
        usermap.insert (it, std::pair<string,User>(object.userid,object));

The code I am using to write the objects in a .bin file is -

map<std::string, User>::iterator it;
for ( it = usermap.begin(); it != usermap.end(); it++ )
{
myfile2 << "Object:" << it->second << "\n";
}

But the error I am getting when I am trying to run the code is -

In file included from /usr/include/c++/4.8.2/iostream:39:0, from a3part2_5.cpp:2: /usr/include/c++/4.8.2/ostream:548:5: note: template std::basic_ostream& std::operator<<(std::basic_ostream&, const unsigned char*) operator<<(basic_ostream& __out, const unsigned char* __s) ^ /usr/include/c++/4.8.2/ostream:548:5: note: template argument deduction/substitution failed: a3part2_5.cpp:90:31: note: cannot convert ‘it.std::_Rb_tree_iterator<_Tp>::operator->, User> >()->std::pair, User>::second’ (type ‘User’) to type ‘const unsigned char*’ myfile2 << "Obejct: " << it->second << "\n";

Any solutions for resolving the error?

My User class is defined as - 

class User 
{ 
public: 
string userid; string uid; string gid; string gecos; string directory; string shell; 
User() {} 
};

Upvotes: 0

Views: 1621

Answers (2)

J&#243;n&#225;s Bal&#225;zs
J&#243;n&#225;s Bal&#225;zs

Reputation: 809

An example:

ostream& operator << (ostream &os, User const& u){
    os << "userid:\t" u.userid << "\n";
    // ...
    return os;
}

Upvotes: 1

sameerkn
sameerkn

Reputation: 2259

User is user-defined class and hence ostream cannot understand your User objects when you do myfile2 << "Object:" << it->second << "\n";

This should help Overloading the << Operator for Your Own Classes.

So you should overload operator << for your class.

Upvotes: 4

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