Streams

String Streams

The istringstream class (#include<sstream>) reads characters from a string, and the ostringstream class writes characters to a string.

Using an istringstream, you can read numbers that are stored in a string by using the >> operator.

string input = "January 23, 1955";
istringstream instr(input);
string month;
int day;
string commma.
int year;
instr >> month >> day >> comma >> year;

Note that this input statement yields a day and year as integers. Had we taken the string apart with substr, we would have obtained only strings.
Converting strings that contain digits to their integer values is such a common operation that it is useful to write a helper function for that purpose.
```
int string_to_int(string s)
{
   istringstream instr(s);
   int n;
   instr >> n;
   return n;
}
```

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