std::strstream::strstream(3)

💖 std::strstream::strstream(3) — C++ Standard Libary bestie briefing 💖

okay so this is the std::strstream::strstream(3) page from the C++ Standard Libary, and we are getting into constructor lore. It’s giving “old-school C++ stream energy,” and yes, bestie, the deprecation/removal notes are absolutely part of the story. 💅

🌸 NAME 🌸

std::strstream::strstream — std::strstream::strstream

✨ Synopsis ✨

Two constructor overloads, both with big deprecated in C++98 / removed in C++26 energy.

strstream();

Overload (1): deprecated in C++98, removed in C++26.

strstream( char* s, int n, std::ios_base::openmode mode =
                               std::ios_base::in |
                               std::ios_base::out );

Overload (2): also deprecated in C++98 and removed in C++26.

This constructs a new input/output strstream and its underlying std::strstreambuf. 🫶

1. Default-constructs the underlying std::strstreambuf, which creates a dynamically growing buffer, and initializes the base class with the address of the strstreambuf member.
2. Initializes the base class with the address of the underlying std::strstreambuf member, which is initialized in one of the two possible ways below, and both of them use a user-provided fixed-size array:
   • a) if (mode & app) == 0 (the app bit is not set in mode), constructs the buffer by calling strstreambuf(s, n, s). The behavior is undefined if there are less than n elements in the array whose first element is pointed to by s.
   • b) if (mode & app) != 0 (the app bit is set in mode), constructs the buffer by calling strstreambuf(s, n, s + std::strlen(s)). The behavior is undefined if there are less than n elements in the array whose first element is pointed to by s or if the array does not contain a valid null-terminated character sequence.

🎀 Parameters 🎀

• s — char array to use as the output buffer.
• n — size of the array to be used for output.
• mode — specifies stream open mode. It is a bitmask type, and the following constants are defined (although only app is used):
  • app — seek to the end of stream before each write.
  • binary — open in binary mode.
  • in — open for reading.
  • out — open for writing.
  • trunc — discard the contents of the stream when opening.
  • ate — seek to the end of stream immediately after open.
  • noreplace (C++23) — open in exclusive mode.

💅 Example 💅

The page says // Run this code, so here is the whole example, bestie:

#include <iostream>
#include <string>
#include <strstream>

int main()
{
    // dynamic buffer
    std::strstream s1;
    s1 << 1 << ' ' << 3.14 << " example" << std::ends;
    std::cout << "Buffer holds: '" << s1.str() << "'\n";
    s1.freeze(false);

    int n;
    double d;
    std::string w;
    s1 >> n >> d >> w;
    std::cout << "Read back: n = " << n
              << ", d = " << d
              << ", w = '" << w << "'\n";

    // static buffer
    char arr[20] = "-1 -3.14 ";
    std::strstream s2(arr, sizeof arr, std::ios_base::app);
    s2 << "another" << std::ends;
    std::cout << "Buffer holds: '" << s2.str() << "'\n";
    s2 >> n >> d >> w;
    std::cout << "Read back: n = " << n
              << ", d = " << d
              << ", w = '" << w << "'\n";
}

🫶 Output 🫶

Buffer holds: '1 3.14 example'
Read back: n = 1, d = 3.14, w = 'example'
Buffer holds: '-1 -3.14 another'
Read back: n = -1, d = -3.14, w = 'another'

🌀 Defect reports 🌀

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

• DR LWG 115 — applied to C++98. Behavior as published: overload (2) only considered the case mode & app == 0 (== has higher precedence than &). Correct behavior: considers cases (mode & app) == 0 and (mode & app) != 0.

🔥 See also 🔥

• constructor — constructs a strstreambuf object (public member function of std::strstreambuf).
• constructor — constructs an istrstream object, optionally allocating the buffer (public member function of std::istrstream).
• constructor — constructs an ostrstream object, optionally allocating the buffer (public member function of std::ostrstream).

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okay bestie, that’s the whole page! Source/version energy: http://cppreference.com, dated 2024.06.10, and the page is std::strstream::strstream(3). Periodt. 💖✨