How to iterate over a std::map full of strings in C++

Your main problem is that you are calling a method called first() in the iterator. What you are meant to do is use the property called first:

...append(iter->first) rather than ...append(iter->first())

As a matter of style, you shouldn't be using new to create that string.

std::string something::toString() 
{
        std::map<std::string, std::string>::iterator iter;
        std::string strToReturn; //This is no longer on the heap

        for (iter = table.begin(); iter != table.end(); ++iter) {
           strToReturn.append(iter->first); //Not a method call
           strToReturn.append("=");
           strToReturn.append(iter->second);
           //....
           // Make sure you don't modify table here or the iterators will not work as you expect
        }
        //...
        return strToReturn;
}

edit: facildelembrar pointed out (in the comments) that in modern C++ you can now rewrite the loop

for (auto& item: table) {
    ...
}

1. Don't write a toString() method. This is not Java. Implement the stream operator for your class.

2. Prefer using the standard algorithms over writing your own loop. In this situation, std::for_each() provides a nice interface to what you want to do.

3. If you must use a loop, but don't intend to change the data, prefer const_iterator over iterator. That way, if you accidently try and change the values, the compiler will warn you.

Then:

std::ostream& operator<<(std::ostream& str,something const& data)
{
    data.print(str)
    return str;
}

void something::print(std::ostream& str) const
{
    std::for_each(table.begin(),table.end(),PrintData(str));
}

Then when you want to print it, just stream the object:

int main()
{
    something    bob;
    std::cout << bob;
}

If you actually need a string representation of the object, you can then use lexical_cast.

int main()
{
    something    bob;

    std::string  rope = boost::lexical_cast<std::string>(bob);
}

The details that need to be filled in.

class somthing
{
    typedef std::map<std::string,std::string>    DataMap;
    struct PrintData
    {
         PrintData(std::ostream& str): m_str(str) {}
         void operator()(DataMap::value_type const& data) const
         {
             m_str << data.first << "=" << data.second << "\n";
         }
         private:  std::ostream& m_str;
    };
    DataMap    table;
    public:
        void something::print(std::ostream& str);
};

Change your append calls to say

...append(iter->first)

and

... append(iter->second)

Additionally, the line

std::string* strToReturn = new std::string("");

allocates a string on the heap. If you intend to actually return a pointer to this dynamically allocated string, the return should be changed to std::string*.

Alternatively, if you don't want to worry about managing that object on the heap, change the local declaration to

std::string strToReturn("");

and change the 'append' calls to use reference syntax...

strToReturn.append(...)

instead of

strToReturn->append(...)

Be aware that this will construct the string on the stack, then copy it into the return variable. This has performance implications.

Note that the result of dereferencing an std::map::iterator is an std::pair. The values of first and second are not functions, they are variables.

Change:

iter->first()

to

iter->first

Ditto with iter->second.