std::ostrstream::ostrstream

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

ostrstream();	(1)
ostrstream(char* s, int n, std::ios_base::openmode mode = std::ios_base::out);	(2)

Constructs new output strstream and its underlying std::strstreambuf.

1) Default-constructs the underlying std::strstreambuf, which creates a dynamically growing buffer, and initializes the base class with the address of the strstreambuf member.

2) Initialized the base class with the address of the underlying std::strstreambuf member, which is initialized in one of the two possible ways, both of which write to user-provided fixed-size array:

a) if the app bit is not set in mode, constructs the buffer by calling strstreambuf(s, n, s). The behavior is undefined if there are less than n elements in the array whose first element is pointed to by s

b) if the app bit is set in mode, constructs the buffer by calling strstreambuf(s, n, s + std::strlen(s)). The behavior is undefined if there are less than n elements in the array whose first element is pointed to by s or if the array does not contain a valid null-terminated character sequence.

Parameters

s	-	char array to use as the output buffer
n	-	size of the array to be used as the output buffer
mode	-	specifies stream open mode. It is a bitmask type, the following constants are defined (although only app is used): Constant Explanation app seek to the end of stream before each write binary open in binary mode in open for reading out open for writing trunc discard the contents of the stream when opening ate seek to the end of stream immediately after open

Example

Run this code

#include <iostream>
#include <strstream>

int main()
{
    std::ostrstream s1; // dynamic buffer
    s1 << 1 << ' ' << 3.14 << " example\n" << std::ends;
    std::cout << s1.str();
    s1.freeze(false);

    char arr[15] = "Hello";

    std::ostrstream s2(arr, sizeof arr, std::ios_base::app);
    s2 << ", world!" << std::ends;
    std::cout << s2.str() << '\n';
    std::cout << arr << '\n'; // streams use the provided arrays
}

Output:

1 3.14 example
Hello, world!
Hello, world!

See also

(constructor)	constructs a strstreambuf object (public member function of std::strstreambuf)
(constructor)	constructs an strstream, optionally allocating the buffer (public member function of std::istrstream)
(constructor)	constructs an strstream, optionally allocating the buffer (public member function of std::strstream)