std::ostrstream::str

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Input/output library

I/O manipulators

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

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

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::ostrstream

Member functions

ostrstream::ostrstream

ostrstream::~ostrstream

ostrstream::rdbuf

ostrstream::str

ostrstream::freeze

ostrstream::pcount

 

char* str();

Returns the pointer to the beginning of the buffer, after freezing it. Effectively calls rdbuf()->str()

Notes

Before a call to str() that uses the result as a C string, the stream buffer must be null-terminated. Regular output such as with stream << 1.2 does not store a null terminator, it must be appended explicitly, typically with the manipulator std::ends.

After a call to str(), dynamic streams become frozen. A call to freeze(false) is required before exiting the scope in which this ostrstream object was created. otherwise the destructor will leak memory. Also, additional output to a frozen stream may be truncated once it reaches the end of the allocated buffer, which may leave the buffer not null-terminated.

Parameters

(none)

Return value

Pointer to the beginning of the buffer in the associated std::strsteambuf or NULL if no buffer is available.

Example

Run this code

#include <strstream>
#include <iostream>
 
int main()
{
    std::ostrstream dyn; // dynamically-allocated output buffer
    dyn << "Test: " << 1.23; // not adding std::ends to demonstrate append behavior
    std::cout << "The output stream holds \"";
    std::cout.write(dyn.str(), dyn.pcount()) << "\"\n"; 
    // the stream is now frozen due to str()
    dyn << " More text" << std::ends;
    std::cout << "The output stream holds \"";
    std::cout.write(dyn.str(), dyn.pcount()) << "\"\n";
    dyn.freeze(false);
}

Possible output:

The stream holds "Test: 1.23"
The stream holds "Test: 1.23 More "

See also

str	marks the buffer frozen and returns the beginning pointer of the input sequence (public member function of std::strstreambuf)