Re: Missing values in getter

From:

Thomas Maeder <maeder@glue.ch>

Newsgroups:

comp.lang.c++.moderated

Date:

Mon, 3 Dec 2007 17:17:25 CST

Message-ID:

<m2zlwrww47.fsf@glue.ch>

Xavier Pegenaute <xpegenaute@gmail.com> writes:

#include <map>
#include <string>
#include <iostream>
using namespace std;

class Test {
private:
         map<string, string> values;
public:
         Test();
         const map<string, string> get_values() const;
};

Test::Test(){
         values["A"]="One";
         values["B"]="Two";
         values["C"]="Three";
         values["D"]="Four";
}

const map<string, string> Test::get_values() const{
         return values;
}

This returns a copy of the values data member.

int main(){
  Test t;
  cout<<"-----------First test---------"<<endl;
  cout<<"Size: "<<t.get_values().size()<<endl;
  map<string, string>::const_iterator it1 = t.get_values().begin();
  while(it1 != t.get_values().end()){

Each time t.get_values() is evaluated on these lines, you obtain a
different map object; this object will be destructed at the end of the
"full expression" that causes it to be created (read: at the end of
the line).

In the expression it1 != t.get_values().end(), it1 therefore refers
into a map object that has already been destructed again; comparing
it1's value to another iterator's causes your program to have
undefined behavior.

    cout<<it1->first<<" "<<it1->second<<endl;
    it1++;
  }

[snip]

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