# std::basic_stringbuf<CharT,Traits,Allocator>::basic_stringbuf

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< cpp‎ | io‎ | basic stringbuf

basic_stringbuf() : basic_stringbuf(std::ios_base::in | std::ios_base::out) { } | (1) |
| (2) |
explicit basic_stringbuf( std::ios_base::openmode which = std::ios_base::in | std::ios_base::out ); |  | (until C++11)
explicit basic_stringbuf( std::ios_base::openmode which ); |  | (since C++11)
explicit basic_stringbuf( const std::basic_string<CharT, traits, Allocator>& new_str, std::ios_base::openmode which = std::ios_base::in | std::ios_base::out ); | (3) |
basic_stringbuf( const basic_stringbuf& rhs ) = delete; | (4) | (since C++11)
basic_stringbuf( basic_stringbuf&& rhs ); | (5) | (since C++11)

1) Default constructor. It is implementation-defined whether the sequence pointers (`eback()`, `gptr()`, `egptr()`, `pbase()`, `pptr()`, `epptr()`) are initialized to null pointers.
2) Constructs a `std::basic_stringbuf` object: initializes the base class by calling the default constructor of std::basic_streambuf, initializes the character sequence with an empty string, and sets the mode to `which`.
3) Constructs a `std::basic_stringbuf` object by performing the same initialization as 1), followed by initializing the associated character sequence as if by calling str(new_str).
4) The copy constructor is deleted; `std::basic_stringbuf` is not CopyConstructible
5) Move-constructs a `std::basic_stringbuf` object by moving all state from another `std::basic_stringbuf` object `rhs`, including the associated string, the open mode, the locale, and all other state. After the move, the six pointers of std::basic_streambuf in *this are guaranteed to be different from the corresponding pointers in the moved-from `rhs` unless null.

### Parameters

new_str | - | a `basic_string` used to initialize the buffer
rhs | - | another `basic_stringbuf`
which | - | specifies stream open mode. It is bitmask type, the following constants are defined:
Constant | Explanation
`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

### Notes

Typically called by the constructor of std::basic_stringstream.

The level of support for the open modes other than std::ios_base::in and std::ios_base::out varies among implementations. C++11 explicitly specifies the support for std::ios_base::ate in str() and in this constructor, but std::ios_base::app, std::ios_base::trunc, and std::ios_base::binary have different effects on different implementations.

### Defect reports

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

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
P0935R0 | C++11 | default constructor was explicit | made implicit

### Example

Demonstrates calling the constructor of basic_stringbuf directly.

Run this code

    #include <iostream>
    #include <sstream>

    int main()
    {
        // default constructor (mode = in|out)
        std::stringbuf buf1;
        buf1.sputc('1');
        std::cout << &buf1 << '\n';

        // string constructor in at-end mode (C++11)
        std::stringbuf buf2("test", std::ios_base::in
                                  | std::ios_base::out
                                  | std::ios_base::ate);
        buf2.sputc('1');
        std::cout << &buf2 << '\n';

        // append mode test (results differ among compilers)
        std::stringbuf buf3("test", std::ios_base::in
                                  | std::ios_base::out
                                  | std::ios_base::app);
        buf3.sputc('1');
        buf3.pubseekpos(1);
        buf3.sputc('2');
        std::cout << &buf3 << '\n';
    }

Output:

    1
    test1
    est12 (Sun Studio) 2st1 (GCC)

### See also

(constructor) | constructs the string stream (public member function of `std::basic_stringstream<CharT,Traits,Allocator>`)

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