std::strstream::strstream
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C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Input/output library
Print functions (C++23)
Buffers
(C++23)
(C++98/26*)
(C++20)
Streams
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File I/O
String I/O
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(C++23)
(C++23)
(C++23)
(C++98/26*)
(C++98/26*)
(C++98/26*)
Synchronized Output
(C++20)
Types
Error category interface
(C++11)
(C++11)
std::strstream
Member functions
strstream::strstream
strstream();
(1)
(deprecated in C++98) (removed in C++26)
strstream( char* s, int n, std::ios_base::openmode mode =
std::ios_base::in | std::ios_base::out );
(2)
(deprecated in C++98) std::ios_base::in | std::ios_base::out );
(removed in C++26)
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.
Contents
[edit] 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
[edit] Example
Run this code
#include <iostream> #include <string> #include <strstream> 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'
[edit] 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 |
[edit] See also
constructs an
(public member function of
istrstream object, optionally allocating the buffer (public member function of
std::istrstream) [edit]
constructs an
(public member function of
ostrstream object, optionally allocating the buffer (public member function of
std::ostrstream) [edit]