C++23 Library - <spanstream> Header

The <spanstream> header is a new addition to C++ 23 Standard Libraries Collection. It provides fixed character buffer streams for input and output.

It is a collection of classes and function templates that let you manipulate letter stretch as if they were streams, much like <stringstream> or <istringstream>. However, it works with std::span<char> rather than pulling from or writing to a string or buffer.

The following image illustrates the inheritance diagram of the <spanstream> header file:

Syntax to include <spanstream>

#include <spanstream>

The above statement imports all the function and class templates of the <spanstream> header in the std namespace of our program.

Class Templates in <spanstream>

Following is the list of classes defined inside the <spanstream> header file:

1. basic_spanbuf
2. basic_ispanstream
3. basic_ospanstream
4. basic_spanstream
5. spanbuf
6. wspanbuf
7. ispanstream
8. wispanstream
9. spanstream
10. wspanstream

All these classes have their own member functions and work. 

std::spanstream

The std:;spanstream is a typedef name defined for basic_spanstream<char> that is nothing but a span-based string I/O buffer. We can initialize the objects of this class using std::span objects and then we can use it like a separate string buffer for input and output.

Example of <spanstream>

The following C Program demonstrates the use of spanstream class:

// C Program to demonstrate the use of spanstream
#include <iostream>
#include <spanstream>

int main()
{
    // A string with some data
    std::string data = "3.45 5.67 4.64";

    // A span<char> from the string
    std::span<char> inSpan(data);

    // creating a spanstream object initialized with spn
    std::spanstream inSpanStream(inSpan);

    // Use the >> operator to read three double values from
    // the spanstream
    double geeks_double1, geeks_double2, geeks_double3;
    inSpanStream >> geeks_double1 >> geeks_double2
        >> geeks_double3;

    // Print out the value of double1, double2 and double3
    std::cout << "geeks_double1 = " << geeks_double1
              << "\n";
    std::cout << "geeks_double2 = " << geeks_double2
              << "\n";
    std::cout << "geeks_double3 = " << geeks_double3
              << "\n";

    // Another span container with test string data
    std::string data_t = "This is a test";
    std::span<char> outSpan(data_t);

    //  A spanstream from the span<char>
    std::spanstream outSpanstream(outSpan);

    // Use the << operator to write data to the spanstream
    // just like normal stream
    outSpanstream << "GeeksforGeeks ";

    // Print out the data stored in outSpanstream
    std::cout << "Result: " << outSpanstream.rdbuf()
              << "\n";

    return 0;
}

Output

geeks_double1 = 3.45
geeks_double2 = 5.67
geeks_double3 = 4.64
Result: GeeksforGeeks 

In the above example, we have used spanstream case to perform both input and output using >> and << operators.

Note: The above code can only be run on the compilers with C++ 23 standard support such as GCC 12 and MSVC 19.31 and onwards.