NAME¶

std::basic_stringbuf::basic_stringbuf - std::basic_stringbuf::basic_stringbuf

Synopsis¶

explicit basic_stringbuf( std::ios_base::openmode which =
std::ios_base::in | (until C++11)
std::ios_base::out );
explicit basic_stringbuf( std::ios_base::openmode which ); (since C++11)
basic_stringbuf()
: basic_stringbuf( std::ios_base::in | std::ios_base::out (2) (since C++11)
) {}
explicit

basic_stringbuf( const std::basic_string<CharT, Traits,
Allocator>& s, (3)
std::ios_base::openmode which =

std::ios_base::in |
std::ios_base::out );
explicit basic_stringbuf( std::basic_string<CharT, Traits,
Allocator>&& s,

std::ios_base::openmode which = (4) (since C++20)

std::ios_base::in |
std::ios_base::out );
basic_stringbuf( std::ios_base::openmode which, const (5) (since C++20)
Allocator& a );
explicit basic_stringbuf( const Allocator& a )
: basic_stringbuf( std::ios_base::in | (6) (since C++20)
std::ios_base::out, a ) {}
template< class SAlloc >

explicit basic_stringbuf( const std::basic_string<CharT,
Traits, SAlloc>& s, (7) (since C++20)
std::ios_base::openmode which =

std::ios_base::in |
std::ios_base::out ); (1)
template< class SAlloc >

basic_stringbuf( const std::basic_string<CharT, Traits,
SAlloc>& s, (8) (since C++20)

std::ios_base::openmode which, const
Allocator& a );
template< class SAlloc >

basic_stringbuf( const std::basic_string<CharT, Traits,
SAlloc>& s, (9) (since C++20)
const Allocator& a )

: basic_stringbuf( s, std::ios_base::in |
std::ios_base::out, a ) {}
template< class StringViewLike >

explicit basic_stringbuf( const StringViewLike& t,
std::ios_base::openmode which = (10) (since C++26)

std::ios_base::in |
std::ios_base::out );
template< class StringViewLike >

basic_stringbuf( const StringViewLike& t, (11) (since C++26)

std::ios_base::openmode which, const
Allocator& a );
template< class StringViewLike >
basic_stringbuf( const StringViewLike& t, const Allocator& a (12) (since C++26)
);
basic_stringbuf( basic_stringbuf&& rhs ); (13) (since C++11)
basic_stringbuf( basic_stringbuf&& rhs, const Allocator& a ); (14) (since C++20)
basic_stringbuf( const basic_stringbuf& rhs ) = delete; (15) (since C++11)

The std::basic_streambuf base and the exposition-only data members buf and mode are
initialized as follows.

After initializing these subobjects, overloads (3-12) initialize the input and
output sequences as if by calling init_buf_ptrs().

Overload std::basic_streambuf buf mode
base
(1) which
implementation-defined std::ios_base::in |
(2) (see below)
std::ios_base::out
(3) s
(4) std::move(s) which
(5)
a std::ios_base::in |
(6)
default-initialized std::ios_base::out
(7) s which
(8)
{s, a} std::ios_base::in |
(9)
std::ios_base::out
(10) {sv, Allocator()} which
(11)
{sv, a} std::ios_base::in |
(12)
std::ios_base::out
(13) rhs std::move(rhs).str()
(14) (copy constructed) {std::move(rhs).str(), rhs.mode
a}

1,2) Overload
(1)
(until C++11)
(2)
(since C++11) is the default constructor. It is implementation-defined whether the
sequence pointers (eback(), gptr(), egptr(), pbase(), pptr(), epptr()) are
initialized to null pointers.
5,6) When the construction is complete, str.empty() is true.
7) This overload participates in overload resolution only if std::is_same_v<SAlloc,
Allocator> is false.
10-12) Implicitly converts t to a string view sv as if by
std::basic_string_view<CharT, Traits> sv = t;, then it is used as above in the
table.
These overloads participate in overload resolution only if
std::is_convertible_v<const StringViewLike&,
std::basic_string_view<CharT, Traits>> is true.
13,14) Overload (13) is the move constructor. It is implementation-defined whether
the six sequence pointers in *this obtain the values which rhs had.
When the construction is complete, rhs is empty but usable, and
* Let rhs_p refer to the state of rhs just prior to this construction, the
following expressions will evaluate to true:

* str() == rhs_p.str()
* getloc() == rhs_p.getloc()
* gptr() - eback() == rhs_p.gptr() - rhs_p.eback()
* egptr() - eback() == rhs_p.egptr() - rhs_p.eback()
* pptr() - pbase() == rhs_p.pptr() - rhs_p.pbase()
* epptr() - pbase() == rhs_p.epptr() - rhs_p.pbase()
* Let rhs_a refer to the state of rhs just after this construction, the following
expressions will evaluate to true:

* !eback() || eback() != rhs_a.eback()
* !gptr() || gptr() != rhs_a.gptr()
* !egptr() || egptr() != rhs_a.egptr()
* !pbase() || pbase() != rhs_a.pbase()
* !pptr() || pptr() != rhs_a.pptr()
* !epptr() || epptr() != rhs_a.epptr()
15) The copy constructor is deleted; std::basic_stringbuf is not CopyConstructible.

Parameters¶

s - a std::basic_string used to initialize the buffer
t - an object (convertible to std::basic_string_view) used to initialize the
buffer
a - another allocator used to construct the internal std::basic_string
rhs - another basic_stringbuf
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
which - 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

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.

Feature-test macro Value Std Feature
__cpp_lib_sstream_from_string_view 202306L (C++26) Interfacing string streams with
std::string_view

Example¶

Demonstrates calling the constructor of std::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)

Defect reports

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

DR Applied to Behavior as published Correct behavior
1. overload (1) allocated no array object 1. removed the
LWG 432 C++98 2. overload (3) did not specify how the limitation
input 2. specified
and output sequences are initialized
overload (3) set epptr() to point one past
LWG 562 C++98 the last underlying epptr() can be set
character if bool(which & beyond that position
std::ios_base::out) == true
P0935R0 C++11 the default constructor was explicit made implicit

See also¶

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