NAME¶

std::basic_istringstream::basic_istringstream - std::basic_istringstream::basic_istringstream

Synopsis¶

explicit basic_istringstream( std::ios_base::openmode mode = (until C++11)
std::ios_base::in );
explicit basic_istringstream( std::ios_base::openmode mode ); (since C++11)
basic_istringstream() (2) (since C++11)
: basic_istringstream(std::ios_base::in) {}
explicit basic_istringstream

( const std::basic_string<CharT, Traits, Allocator>& str, (3)
std::ios_base::openmode mode =

std::ios_base::in );
explicit basic_istringstream

( std::basic_string<CharT, Traits, Allocator>&& str, (4) (since C++20)
std::ios_base::openmode mode =

std::ios_base::in );
basic_istringstream( std::ios_base::openmode mode, const (5) (since C++20)
Allocator& a );
template< class SAlloc >

basic_istringstream( const std::basic_string<CharT, Traits,
SAlloc>& str, (6) (since C++20)

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

basic_istringstream( const std::basic_string<CharT, Traits, (1)
SAlloc>& str, (7) (since C++20)
const Allocator& a )

: basic_istringstream(str, std::ios_base::in, a) {}
template< class SAlloc >

explicit basic_istringstream
( const std::basic_string<CharT, Traits, SAlloc>& str, (8) (since C++20)
std::ios_base::openmode mode =

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

explicit basic_istringstream
( const StringViewLike& t, (9) (since C++26)
std::ios_base::openmode mode =

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

basic_istringstream( const StringViewLike& t, (10) (since C++26)

std::ios_base::openmode mode, const
Allocator& a );
template< class StringViewLike >
basic_istringstream( const StringViewLike& t, const (11) (since C++26)
Allocator& a );
basic_istringstream( basic_istringstream&& other ); (12) (since C++11)

Constructs new string stream.

Given

* base_type as std::basic_istream<CharT, Traits>, and
* buf_type as std::basic_stringbuf<CharT, Traits, Allocator>,

the std::basic_istream base and the exposition-only data member sb are initialized
as follows.

Over std::basic_istream base sb
load
(1) buf_type(mode | std::ios_base::in)
(2) buf_type(std::ios_base::in)
(3) buf_type(str, mode |
std::ios_base::in)
(4) buf_type(std::move(str), mode |
std::ios_base::in)
(5) base_type(std::addressof(sb))^[1] buf_type(mode | std::ios_base::in,
a)
(6) buf_type(str, mode |
std::ios_base::in, a)
(7) buf_type(str, std::ios_base::in,
a)
(8) buf_type(str, mode |
std::ios_base::in)
(9) {t, mode | std::ios_base::in,
std::addressof(sb) Allocator()}
(10) {t, mode | std::ios_base::in, a}
(11) {t, std::ios_base::in, a}
(12) move constructed from other's move constructed from other.sb
std::basic_istream base

1. ↑ The std::basic_iostream base was intialized with base_type(&sb) (for overloads
(1,3)) until C++11.
8) This overload participates in overload resolution only if std::is_same_v<SAlloc,
Allocator> is false.
9-11) These overloads participate in overload resolution only if
std::is_convertible_v<const StringViewLike&, std::basic_string_view<CharT, Traits>>
is true.

Parameters¶

str - string to use as initial contents of the string stream
t - an object (convertible to std::basic_string_view) to use as initial contents
of the string stream
a - allocator used for allocating the contents of the string stream
specifies stream open mode. It is a BitmaskType, the following constants are
defined:

Constant Explanation
app seek to the end of stream before each write
mode - 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
other - another string stream to use as source

Notes¶

Construction of one-off basic_istringstream objects in a tight loop, such as when
used for string conversion, may be significantly more costly than calling str() to
reuse the same object.

Feature-test macro Value Std Feature
__cpp_lib_sstream_from_string_view 202306L (C++26) Interfacing std::stringstreams
with std::string_view, (9-11)

Example¶

// Run this code

#include <iostream>
#include <sstream>

int main()
{
// default constructor (input/output stream)
std::stringstream buf1;
buf1 << 7;
int n = 0;
buf1 >> n;
std::cout << "buf1 = " << buf1.str() << " n = " << n << '\n';

// input stream
std::istringstream inbuf("-10");
inbuf >> n;
std::cout << "n = " << n << '\n';

// output stream in append mode (C++11)
std::ostringstream buf2("test", std::ios_base::ate);
buf2 << '1';
std::cout << buf2.str() << '\n';
}

Output:¶

buf1 = 7 n = 7
n = -10
test1

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 the default constructor was explicit made implicit

See also¶

str gets or sets the contents of underlying string device object
(public member function)
constructs a basic_stringbuf object
constructor (public member function of
std::basic_stringbuf<CharT,Traits,Allocator>)