When should I use `stringstream` instead of `string::append()`?
Supposing I'm going to catenate just strings.

```
stringstream ss;
ss << str1 << "str2" << ...
Write(ss.str());

```

Or:

```
string str;
str.reserve(10000);
str.append(str1);
str.append("str2");
...
Write(str);

```

Which of them is faster?