std::basic_stringbuf::str

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< cpp‎ | io‎ | basic stringbuf
 
C++
 
Input/output library
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(deprecated in C++98)
(C++20)
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String I/O
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(C++11)
(C++11)
 
std::basic_stringbuf
 
std::basic_string<CharT, Traits, Allocator> str() const;
 (1)
void str( const std::basic_string<CharT, Traits, Allocator>& s);
 (2)

Gets and sets the underlying string.

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 the second overload of str(), or from an 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 (since C++11)
2) Deletes the entire underlying character sequence of this std::basic_stringbuf and then configures a new underlying character sequence containing a copy of the contents of s. The pointers of std::basic_streambuf are initialized as follows:
  • For input streams (mode & ios_base::in == true), eback() points at the first character, gptr() == eback(), and egptr() == eback() + s.size(): the subsequent input will read the first character copied from s.
  • For output streams (mode & ios_base::out == true), pbase() points at the first character and epptr() >= pbase() + s.size() (epptr is allowed to point farther so that the following sputc() wouldn't immediately call overflow())
    • For append streams (mode & ios_base::ate == true), pptr() == pbase() + s.size(), so that subsequent output will be appended to the last character copied from s (since C++11)
    • For non-appending output streams, pptr() == pbase(), so that subsequent output will overwrite the characters copied from s.

Parameters

s - a string object holding the replacement character sequence

Return value

1) A string object holding a copy of this buffer's underlying character sequence.
2) (none)

Notes

This function is typically accessed through std::basic_stringstream::str().

Example

Run this code
#include <sstream>
#include <iostream>
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"

See also

 gets or sets the contents of underlying string device object
(public member function of std::basic_stringstream)
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