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

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< cpp‎ | io‎ | basic stringbuf
 
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std::basic_stringbuf
 
basic_stringbuf()
    : basic_stringbuf(std::ios_base::in | std::ios_base::out) { }
 (1)
explicit basic_stringbuf( std::ios_base::openmode which );
 (2)
explicit basic_stringbuf( const std::basic_string<CharT,Traits,Allocator>& s,

                          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)
explicit basic_stringbuf( const Allocator& a )
    : basic_stringbuf(std::ios_base::in | std::ios_base::out, a) { }
 (6) (since C++20)
basic_stringbuf( std::ios_base::openmode which, const Allocator& a );
 (7) (since C++20)
explicit basic_stringbuf( std::basic_string<CharT,Traits,Allocator>&& s,

                          std::ios_base::openmode which =

                              std::ios_base::in | std::ios_base::out );
 (8) (since C++20)
template<class SAlloc>

basic_stringbuf( const std::basic_string<CharT,Traits,SAlloc>& s,
                 const Allocator& a )

    : basic_stringbuf(s, std::ios_base::in | std::ios_base::out, a ) { }
 (9) (since C++20)
template<class SAlloc>

basic_stringbuf( const std::basic_string<CharT,Traits,SAlloc>& s,

                 std::ios_base::openmode, const Allocator& a );
 (10) (since C++20)
template<class SAlloc>

explicit basic_stringbuf( const std::basic_string<CharT, Traits, SAlloc>& s
                          std::ios_base::openmode which =

                              std::ios_base::in | std::ios_base::out );
 (11) (since C++20)
basic_stringbuf( basic_stringbuf&& rhs, const Allocator& a );
 (12) (since C++20)
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(s).
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.
6-7) Same as (1-2), except that a is used to construct the associated string.
8) Same as (3), except that std::move(s) is used to construct the associated string.
9-10) Constructs a std::basic_stringbuf object by performing the same initialization as (1), followed by initializing the associated string with content of s, using a as its allocator.
11) Same as (3), except the type of s's allocator is not Allocator. This overload only participates in overload resolution if SAlloc and Allocator are not the same type.
12) Same as (5), except that a is used to construct the associated string.

Parameters

s - a basic_string used to initialize the buffer
a - another allocator used to construct the internal basic_string
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

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