stringstream
- C++ course
- Intermediate
- Lesson 96/116
- 5 min
Learn bidirectional streams with stringstream.
stringstream in both directions
std::stringstream is used for both reading and writing. It combines the capabilities of istringstream and ostringstream.
Example: std::stringstream ss; ss << "100 200"; int a, b; ss >> a >> b;. Here we first write a string to the stream with <<, then extract the numbers back with >>. This is one tool for the build-a-string-then-parse pattern. The #include <sstream> header suffices. You can get the written content with .str() and set the content to read with .str("...").
The write-then-read pattern
The most common use of stringstream is: first write data with <<, then read it back with >>. This is a practical way to serialize and parse data.
Example: ss << name << " " << age; builds a record. Then ss >> name2 >> age2; reads it back. This pattern is the basis of save and load operations. To reset the content you write ss.clear(); ss.str("");; clear() resets error flags and str("") empties the content.
Practice Write to the stream and read back
Create a std::stringstream. Write "100 200" with <<. Then extract two numbers with >>, sum them and print the total with std::cout.
Starter code
#include <iostream>
#include <sstream>
#include <string>
int main() {
// Write to the stream, read back and sum
return 0;
}Sample solution
#include <iostream>
#include <sstream>
#include <string>
int main() {
std::stringstream ss;
ss << "100 200";
int a, b;
ss >> a >> b;
std::cout << a + b;
return 0;
}Expected output
300
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What can stringstream do?
std::stringstream ss;- Read only
- Write only
- Both read and write Correct answer
- Open files only
Explanation: stringstream can both read and write.
2 Define a stringstream
std::____ ss;std::stringstream ss;Explanation: std::stringstream is a bidirectional stream.
3 Match each piece to its role
| Term | Meaning |
|---|---|
stringstream |
Bidirectional stream |
<< |
Writing to stream |
>> |
Reading from stream |
.clear() |
Flag reset |