std::strstream::strstream

 

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::strstream

Member functions

strstream::strstream

strstream::~strstream

strstream::rdbuf

strstream::str

strstream::pcount

strstream::freeze

 

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

Constructs new input/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 use a user-provided fixed-size array:

a) if (mode & app) == 0 (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 (mode & app) != 0 (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 for output
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 noreplace (C++23) open in exclusive mode

Example

Run this code

#include <iostream>
#include <strstream>
#include <string>
 
int main()
{
    // dynamic buffer
    std::strstream s1;
    s1 << 1 << ' ' << 3.14 << " example" << std::ends;
    std::cout << "Buffer holds: '" << s1.str() << "'\n";
    s1.freeze(false);
 
    int n;
    double d;
    std::string w;
    s1 >> n >> d >> w;
    std::cout << "Read back: n = " << n
              << ", d = " << d
              << ", w = '" << w << "'\n";
 
    // static buffer
    char arr[20] = "-1 -3.14 ";
    std::strstream s2(arr, sizeof arr, std::ios_base::app);
    s2 << "another" << std::ends;
    std::cout << "Buffer holds: '" << s2.str() << "'\n";
    s2 >> n >> d >> w;
    std::cout << "Read back: n = " << n
              << ", d = " << d
              << ", w = '" << w << "'\n";
}

Output:

Buffer holds: '1 3.14 example'
Read back: n = 1, d = 3.14, w = 'example'
Buffer holds: '-1 -3.14 another'
Read back: n = -1, d = -3.14, w = 'another'

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 115	C++98	overload (2) only considered the case mode & app == 0 (== has higher precedence than &)	considers cases (mode & app) == 0 and (mode & app) != 0

See also

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