std::stringstream (from <sstream>) is a stream whose buffer is a string — use it to parse text with >> or to build strings with <<.

Parsing

C++

#include <iostream>
#include <sstream>
#include <string>
#include <vector>

int main() {
    std::istringstream in("3 4.5 hello 7");
    int a; double b; std::string word; int c;
    in >> a >> b >> word >> c;
    std::cout << a + c << ' ' << b << ' ' << word << '\n';

    std::string line = "10,20,30";
    std::stringstream ss(line);
    std::vector<int> nums;
    for (std::string tok; std::getline(ss, tok, ',');) nums.push_back(std::stoi(tok));
    std::cout << nums.size() << ' ' << nums[2] << '\n';

    std::istringstream bad("12abc");
    int n; std::string rest;
    bad >> n >> rest;                     // reads 12, then "abc"
    std::cout << n << ' ' << rest << '\n';

    std::istringstream words("  the   quick brown  ");
    int count = 0;
    for (std::string w; words >> w;) ++count;
    std::cout << count << " words\n";
}

Output

10 4.5 hello
3 30
12 abc
3 words

Building strings

C++

#include <iomanip>
#include <iostream>
#include <sstream>
#include <string>

std::string toHex(int value) {
    std::ostringstream os;
    os << "0x" << std::hex << std::setw(4) << std::setfill('0') << value;
    return os.str();
}

int main() {
    std::ostringstream report;
    report << "total=" << 42 << ", ratio=" << std::fixed << std::setprecision(2) << 0.4567;
    std::cout << report.str() << '\n';
    std::cout << toHex(255) << '\n';

    report.str("");                        // reuse: reset the contents…
    report.clear();                        // …and the state flags
    report << "fresh";
    std::cout << report.str() << '\n';
}

Output

total=42, ratio=0.46
0x00ff
fresh

Class	Direction
`std::istringstream`	Read from a string (`>>`, `getline`)
`std::ostringstream`	Write into a string (`<<`, then `.str()`)
`std::stringstream`	Both

How do you split a string by a delimiter in C++?