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

Question

I have the following issue related to iterating over an associative array of strings defined using `std::map`. ``` -- snip -- class something { //... private: std::map table; //... } ``` In the constructor I populate table with pairs of string keys associated to string data. Somewhere else I have a method `toString` that returns a string object that contains all the keys and associated data contained in the table object(as key=data format). ``` std::string something::toString() { std::map::iterator iter; std::string* strToReturn = new std::string(""); for (iter = table.begin(); iter != table.end(); iter++) { strToReturn->append(iter->first()); strToReturn->append('='); strToRetunr->append(iter->second()); //.... } //... } ``` When I'm trying to compile I get the following error: ``` error: "error: no match for call to ‘(std::basic_string, std::allocator >) ()’". ``` Could somebody explain to me what…

Accepted Answer

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) {
    ...
}
```

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

Solution

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