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

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Revision as of 14:39, 12 September 2023 by SmartDev (Talk | contribs)

 
C++
 
Input/output library
 
std::basic_stringbuf
 
(1)
std::basic_string<CharT, Traits, Allocator> str() const;
 (until C++20)
std::basic_string<CharT, Traits, Allocator> str() const&;
 (since C++20)
template<class SAlloc>
std::basic_string<CharT, Traits, SAlloc> str( const SAlloc& a ) const;
 (2) (since C++20)
std::basic_string<CharT, Traits, Allocator> str() &&;
 (3) (since C++20)
void str( const std::basic_string<CharT, Traits, Allocator>& s );
 (4)
template<class SAlloc>
void str( const std::basic_string<CharT, Traits, SAlloc>& s );
 (5) (since C++20)
void str( std::basic_string<CharT, Traits, Allocator>&& s );
 (6) (since C++20)
template< class StringViewLike >
void str( const StringViewLike& t );
 (7) (since C++26)

Gets and sets the underlying string.

In the descriptions below, buf and mode are exposition-only data members of *this.

1) Creates and returns a std::basic_string object containing a copy of this std::basic_stringbuf's underlying character sequence. For input-only streams, the returned string contains the characters from the range [eback(), egptr()). For input/output or output-only streams, contains the characters from pbase() to the last character in the sequence regardless of egptr() and epptr().
The member character sequence in a buffer open for writing can be over-allocated for efficiency purposes. In that case, only the initialized characters are returned: these characters are the ones that were obtained from the string argument of the constructor, the string argument of the most recent call to a setter overload of str(), or from a write operation. A typical implementation that uses over-allocation maintains a high-watermark pointer to track the end of the initialized part of the buffer and this overload returns the characters from pbase() to the high-watermark pointer.
Equivalent to return std::basic_string<CharT, Traits, Allocator>(view(), get_allocator());.
(since C++20)
2) Same as (1), except that a is used to construct the returned std::basic_string. Equivalent to return std::basic_string<CharT, Traits, SAlloc>(view(), a);.
This overload participates in overload resolution only if SAlloc meets the requirements of Allocator.
3) Creates a std::basic_string object as if by move constructing it from *this's underlying character sequence in buf. buf may need to be adjusted to contain the same content as in (1) at first. After that, sets buf to empty and calls init_buf_ptrs(), then returns the std::basic_string object.
4) Replaces the underlying character sequence as if by buf = s, then calls init_buf_ptrs().
5) Same as (4), except the type of s's allocator is not Allocator.
This overload participates in overload resolution only if std::is_same_v<SAlloc, Allocator> is false.
6) Replaces the underlying character sequence as if by buf = std::move(s), then calls init_buf_ptrs().
7) Implicitly converts t to a string view sv as if by std::basic_string_view<CharT, Traits> sv = t;, then replaces the underlying character sequence as if by buf = sv, then calls init_buf_ptrs().
This overload participates in overload resolution only if std::is_convertible_v<const StringViewLike&,
                      std::basic_string_view<CharT, Traits>> is true.

Contents

Parameters

s - a std::basic_string object holding the replacement character sequence
t - an object (convertible to std::basic_string_view) holding the replacement character sequence
a - allocator to use for all memory allocations of the returned std::basic_string

Return value

1-3) A std::basic_string object holding this buffer's underlying character sequence.
4-7) (none)

Notes

This function is typically accessed through std::basic_istringstream::str(), std::basic_ostringstream::str(), or std::basic_stringstream::str().

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

Example

Run this code
#include <iostream>
#include <sstream>
 
int main()
{
    int n;
 
    std::istringstream in;  // could also use in("1 2")
    in.rdbuf()->str("1 2"); // set the get area
    in >> n;
    std::cout << "after reading the first int from \"1 2\", the int is " 
              << n << ", str() = \"" << in.rdbuf()->str() << "\"\n"; // or in.str()
 
    std::ostringstream out("1 2");
    out << 3;
    std::cout << "after writing the int '3' to output stream \"1 2\""
              << ", str() = \"" << out.str() << "\"\n";
 
    std::ostringstream ate("1 2", std::ios_base::ate); // C++11
    ate << 3;
    std::cout << "after writing the int '3' to append stream \"1 2\""
              << ", str() = \"" << ate.str() << "\"\n";
}

Output: 

after reading the first int from "1 2", the int is 1, str() = "1 2"
after writing the int '3' to output stream "1 2", str() = "3 2"
after writing the int '3' to append stream "1 2", str() = "1 23"

Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 432 C++98 1. overload (1) did not specify the content
of the underlying character sequence
2. overload (4) did not specify how the
input and output sequences are initialized 		both specified
LWG 562 C++98 overload (4) set epptr() to point one past the last underlying
character if bool(mode & std::ios_base::out) == true 		epptr() can be set
beyond that position

See also

 gets or sets the contents of underlying string device object
(public member function of std::basic_stringstream<CharT,Traits,Allocator>) [edit]
(C++20)
 obtains a view over the underlying character sequence
(public member function) [edit]
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