std::strstreambuf::str

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Input/output library

I/O manipulators

Print functions (C++23)

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

basic_spanbuf (C++23)

strstreambuf (deprecated in C++98)

basic_syncbuf (C++20)

Streams

Abstractions

ios_base

basic_ios

basic_istream

basic_ostream

basic_iostream

File I/O

basic_ifstream

basic_ofstream

basic_fstream

String I/O

basic_istringstream

basic_ostringstream

basic_stringstream

Array I/O

basic_ispanstream (C++23)

basic_ospanstream (C++23)

basic_spanstream (C++23)

istrstream (deprecated in C++98)

ostrstream (deprecated in C++98)

strstream (deprecated in C++98)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

 

std::strstreambuf

Public member functions

strstreambuf::strstreambuf

strstreambuf::~strstreambuf

strstreambuf::freeze

strstreambuf::str

strstreambuf::pcount

Protected member functions

strstreambuf::underflow

strstreambuf::pbackfail

strstreambuf::overflow

strstreambuf::setbuf

strstreambuf::seekoff

strstreambuf::seekpos

 

char* str();

Calls freeze(), then returns a copy of start pointer of the get area, std::streambuf::eback().

The start of the get area, for all writeable std::strstreambuf objects constructed through the interface provided by std::strstream, is also the start of the put area.

Parameters

(none)

Return value

A copy of eback(), which may be a null pointer.

Notes

This function is typically called through the std::strstream interface.

The call to freeze() guarantees that the returned pointer remains valid until the next explicit call to freeze(false): otherwise (on a dynamic buffer) any output operation could trigger buffer reallocation which would invalidate the pointer. It also causes a memory leak in the destructor of std::strstreambuf, unless freeze(false) is called before the buffer (or, more commonly, the std::strstream that manages it) is destroyed.

Example

Run this code

#include <iostream>
#include <strstream>
 
int main()
{
    std::strstream dyn; // dynamically-allocated read/write buffer
    dyn << "Test: " << 1.23 << std::ends;
    std::strstreambuf* buf = dyn.rdbuf();
    std::cout << "R/W buffer holds [" << buf->str() // or dyn.str()
              << "]\n";
    dyn.freeze(false); // after calling .str() on a dynamic strstream
 
    char arr[10];
    std::ostrstream user(arr, 10); // fixed-size write-only buffer
    buf = user.rdbuf();
    user << 1.23 << std::ends;
    std::cout << "Write-only buffer holds [" << buf->str() // or user.str()
              << "]\n";
 
    std::istrstream lit("1 2 3"); // fixed-size read-only buffer
    buf = lit.rdbuf();
    std::cout << "Read-only buffer holds [" << buf->str() // or lit.str()
              << "]\n";
}

Output:

R/W buffer holds [Test: 1.23]
Write-only buffer holds [1.23]
Read-only buffer holds [1 2 31 2 3]

See also

str	accesses the output buffer (public member function of std::strstream)
str	accesses the output buffer (public member function of std::ostrstream)
str	accesses the output buffer (public member function of std::istrstream)