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

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.

#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"

[edit] 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

[edit] See also

str

gets or sets the contents of underlying string device object
(public member function of std::basic_stringstream<CharT,Traits,Allocator>) [edit]

view

(C++20)

obtains a view over the underlying character sequence
(public member function) [edit]

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

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