sstream

Header: <sstream>

The <sstream> header in C++ provides string stream classes that allow string-based stream operations. It's part of the Standard Template Library (STL) and offers a convenient way to perform input/output operations on strings, similar to how we work with files or console I/O.

Key Characteristics

• Provides classes for string stream operations: istringstream, ostringstream, and stringstream
• Allows treating strings as streams, enabling formatted I/O operations
• Useful for parsing, formatting, and converting between strings and other data types
• Inherits functionality from <istream>, <ostream>, and <iostream>

Example 1: Basic Usage: Parsing Integers from a String

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

int main() {
    std::string input = "10 20 30 40 50";
    std::istringstream iss(input);

    std::vector<int> numbers;
    int num;
    while (iss >> num) {
        numbers.push_back(num);
    }

    std::cout << "Parsed numbers: ";
    for (int n : numbers) {
        std::cout << n << " ";
    }
    std::cout << std::endl;

    return 0;
}

Explanation:

• We create an istringstream object from a string containing space-separated numbers.
• We use a while loop with the stream extraction operator >> to parse integers from the stream.
• Parsed integers are stored in a vector.
• Finally, we print the parsed numbers to verify the result.

Example 2: Formatting Output: Creating a CSV Line

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

int main() {
    std::vector<std::string> data = {"John", "Doe", "30", "New York"};
    std::ostringstream oss;

    for (size_t i = 0; i < data.size(); ++i) {
        oss << data[i];
        if (i < data.size() - 1) {
            oss << ",";
        }
    }

    std::string csv_line = oss.str();
    std::cout << "CSV line: " << csv_line << std::endl;

    return 0;
}

Explanation:

• We use an ostringstream to build a CSV (Comma-Separated Values) line from a vector of strings.
• The << operator is used to insert data into the string stream.
• We add commas between elements, but not after the last element.
• The str() method is called to get the resulting string from the stream.

Example 3: Type Conversion: String to Number and Vice Versa

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

int main() {
    // String to number conversion
    std::string str_num = "123.456";
    std::istringstream iss(str_num);
    double number;
    iss >> number;

    std::cout << "Converted string to number: " << number << std::endl;

    // Number to string conversion with formatting
    double pi = 3.14159265359;
    std::ostringstream oss;
    oss << std::fixed << std::setprecision(2) << pi;
    std::string str_pi = oss.str();

    std::cout << "Converted number to string with 2 decimal places: " << str_pi << std::endl;

    return 0;
}

Explanation:

• We use istringstream to convert a string representation of a number to an actual number (double).
• For the reverse process, we use ostringstream to convert a number to a string.
• We demonstrate how to use I/O manipulators like std::fixed and std::setprecision to format the output.
• The str() method is used to retrieve the formatted string from the output string stream.

Example 4: Mixed Data Parsing: Extracting Different Types

#include <iostream>
#include <sstream>

int main() {
    std::string input = "John 25 180.5";
    std::istringstream iss(input);

    std::string name;
    int age;
    double height;

    iss >> name >> age >> height;

    std::cout << "Name: " << name << std::endl;
    std::cout << "Age: " << age << std::endl;
    std::cout << "Height: " << height << " cm" << std::endl;

    return 0;
}

Explanation:

• We use istringstream to parse a string containing mixed data types.
• The stream extraction operator >> automatically handles type conversion for different variables.
• This example demonstrates how sstream can be used to easily parse structured data from a string.

Additional Considerations

• Error Handling: When using sstream, it's important to check for parsing errors, especially when dealing with user input or external data.
• Performance: For simple string operations, direct string manipulation might be faster. sstream is more useful for complex formatting or parsing tasks.
• Memory Usage: stringstream objects can be reused by calling the clear() and str("") methods, which can be more efficient than creating new objects for each operation.

Summary

The <sstream> header in C++ provides powerful tools for string-based stream operations. It includes istringstream for input operations, ostringstream for output operations, and stringstream for both input and output. These classes are particularly useful for parsing strings, formatting output, and performing type conversions between strings and other data types.

Key applications of <sstream> include: 1. Parsing structured data from strings 2. Formatting data into strings with precise control 3. Performing type conversions between strings and numeric types 4. Building complex strings from various data types

By leveraging the familiar stream interface, <sstream> allows developers to apply their knowledge of I/O operations to string manipulation tasks, making it a versatile and powerful tool in C++ programming.

Related

• How do I use std::stringstream to parse a string
• What are the common use cases for std::stringstream
• How can I format output using std::stringstream
• What are the differences between std::stringstream and std::istringstream
• How do I read and write strings using std::stringstream