std::ostrstream::freeze

C++

Language

Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Algorithms library

Iterators 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)

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)

ostrstream (deprecated)

strstream (deprecated)

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

void freeze(bool flag = true);

If the stream is using a dynamically-allocated array for output, disables (flag == true) or enables (flag == false) automatic allocation/deallocation of the buffer. Effectively calls rdbuf()->freeze(flag)

Notes

After a call to str(), dynamic streams become frozen automatically. 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.

Parameters

flag

-

desired status

Return value

(none)

Example

Run this code

#include <strstream>
#include <iostream>

int main()
{
    std::ostrstream dyn; // dynamically-allocated output buffer
    dyn << "Test: " << 1.23; // note: no std::ends to demonstrate appending
    std::cout << "The output stream contains \"";
    std::cout.write(dyn.str(), dyn.pcount()) << "\"\n";
    // the stream is now frozen due to str()
    dyn << " More text"; // output to a frozen stream may be truncated
    std::cout << "The output stream contains \"";
    std::cout.write(dyn.str(), dyn.pcount()) << "\"\n";
    dyn.freeze(false); // freeze(false) must be called or the  destructor will leak

    std::ostrstream dyn2; // dynamically-allocated output buffer
    dyn2 << "Test: " << 1.23; // note: no std::ends
    std::cout << "The output stream contains \"";
    std::cout.write(dyn2.str(), dyn2.pcount()) << "\"\n";
    dyn2.freeze(false);   // unfreeze the stream after str()
    dyn2 << " More text" << std::ends; // output will not be truncated (buffer grows)
    std::cout << "The output stream contains \"" << dyn2.str() << "\"\n";
    dyn2.freeze(false); // freeze(false) must be called or the  destructor will leak 
}

Possible output:

The output stream contains "Test: 1.23"
The output stream contains "Test: 1.23 More "
The output stream contains "Test: 1.23"
The output stream contains "Test: 1.23 More text"

See also

freeze

sets/clears the frozen state of the buffer (public member function of std::strstreambuf)