# std::strstreambuf

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< cpp‎ | io

Defined in header `<strstream>` |  |
class strstreambuf : public std::basic_streambuf<char> |  | (deprecated in C++98)

`std::strstreambuf` is a std::basic_streambuf whose associated character sequence is a character array, which may be constant (e.g. a string literal), modifyable but not dynamic (e.g. a stack-allocated array), or dynamic, in which case the `std::strstreambuf` may be allowed to reallocate the array as necessary to accomodate output (e.g. by calling delete[] and new[] or user-provided functions).

Typical implementation of a `std::strstreambuf` holds four private data members:

1) buffer state, a bitmask type which can represent any combination of the four values "allocated" (destructor will deallocate), "constant" (output not allowed), "dynamic" (output may reallocate), or "frozen" (deallocation and reallocation are not allowed)
2) allocated buffer size (the beginning of the buffer does not need a special data member, it may be stored in the inherited pointer eback())
3) pointer to user-provided allocation function
4) pointer to user-provided deallocation function.

### Notes

After any call to `str()` on a stream with a dynamic buffer, a call to `freeze(false)` is required to allow the `strstreambuf` destructor to deallocate the buffer when necessary.

### Member functions

### Public member functions

(constructor) | constructs a strstreambuf object (public member function)
(destructor) [virtual] | destructs a strstreambuf object, optionally deallocating the character array (virtual public member function)
freeze | sets/clears the frozen state of the buffer (public member function)
str | marks the buffer frozen and returns the beginning pointer of the input sequence (public member function)
pcount | returns the next pointer minus the beginning pointer in the output sequence: the number of characters written (public member function)

### Protected member functions

underflow [virtual] | reads a character from the input sequence without advancing the next pointer (virtual protected member function)
pbackfail [virtual] | backs out the input sequence to unget a character (virtual protected member function)
overflow [virtual] | appends a character to the output sequence, may reallocate or initially allocate the buffer if dynamic and not frozen (virtual protected member function)
setbuf [virtual] | attempts to replace the controlled character sequence with an array (virtual protected member function)
seekoff [virtual] | repositions the next pointer in the input sequence, output sequence, or both, using relative addressing (virtual protected member function)
seekpos [virtual] | repositions the next pointer in the input sequence, output sequence, or both using absolute addressing (virtual protected member function)

## Inherited from std::basic_streambuf

### Member types

Member type | Definition
`char_type` | CharT
`traits_type` | Traits; the program is ill-formed if `Traits::char_type` is not `CharT`.
`int_type` | Traits::int_type
`pos_type` | Traits::pos_type
`off_type` | Traits::off_type

### Member functions

(destructor) [virtual] | destructs the basic_streambuf object (virtual public member function of `std::basic_streambuf<CharT,Traits>`)

##### Locales

pubimbue | invokes imbue() (public member function of `std::basic_streambuf<CharT,Traits>`)
getloc | obtains a copy of the associated locale (public member function of `std::basic_streambuf<CharT,Traits>`)

##### Positioning

pubsetbuf | invokes setbuf() (public member function of `std::basic_streambuf<CharT,Traits>`)
pubseekoff | invokes seekoff() (public member function of `std::basic_streambuf<CharT,Traits>`)
pubseekpos | invokes seekpos() (public member function of `std::basic_streambuf<CharT,Traits>`)
pubsync | invokes sync() (public member function of `std::basic_streambuf<CharT,Traits>`)

##### Get area

in_avail | obtains the number of characters immediately available in the get area (public member function of `std::basic_streambuf<CharT,Traits>`)
snextc | advances the input sequence, then reads one character without advancing again (public member function of `std::basic_streambuf<CharT,Traits>`)
sbumpc | reads one character from the input sequence and advances the sequence (public member function of `std::basic_streambuf<CharT,Traits>`)
stossc (deprecated in C++98)(removed in C++17) | advances the input sequence as if by calling sbumpc() and discarding the result (public member function)
sgetc | reads one character from the input sequence without advancing the sequence (public member function of `std::basic_streambuf<CharT,Traits>`)
sgetn | invokes xsgetn() (public member function of `std::basic_streambuf<CharT,Traits>`)

##### Put area

sputc | writes one character to the put area and advances the next pointer (public member function of `std::basic_streambuf<CharT,Traits>`)
sputn | invokes xsputn() (public member function of `std::basic_streambuf<CharT,Traits>`)

##### Putback

sputbackc | puts one character back in the input sequence (public member function of `std::basic_streambuf<CharT,Traits>`)
sungetc | moves the next pointer in the input sequence back by one (public member function of `std::basic_streambuf<CharT,Traits>`)

### Protected member functions

(constructor) | constructs a basic_streambuf object (protected member function)
operator= (C++11) | replaces a basic_streambuf object (protected member function)
swap (C++11) | swaps two basic_streambuf objects (protected member function)

##### Locales

imbue [virtual] | changes the associated locale (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)

##### Positioning

setbuf [virtual] | replaces the buffer with user-defined array, if permitted (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
seekoff [virtual] | repositions the next pointer in the input sequence, output sequence, or both, using relative addressing (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
seekpos [virtual] | repositions the next pointer in the input sequence, output sequence, or both using absolute addressing (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
sync [virtual] | synchronizes the buffers with the associated character sequence (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)

##### Get area

showmanyc [virtual] | obtains the number of characters available for input in the associated input sequence, if known (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
underflow [virtual] | reads characters from the associated input sequence to the get area (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
uflow [virtual] | reads characters from the associated input sequence to the get area and advances the next pointer (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
xsgetn [virtual] | reads multiple characters from the input sequence (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
eback gptr egptr | returns a pointer to the beginning, current character and the end of the get area (protected member function)
gbump | advances the next pointer in the input sequence (protected member function)
setg | repositions the beginning, next, and end pointers of the input sequence (protected member function)

##### Put area

xsputn [virtual] | writes multiple characters to the output sequence (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
overflow [virtual] | writes characters to the associated output sequence from the put area (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)
pbase pptr epptr | returns a pointer to the beginning, current character and the end of the put area (protected member function)
pbump | advances the next pointer of the output sequence (protected member function)
setp | repositions the beginning, next, and end pointers of the output sequence (protected member function)

##### Putback

pbackfail [virtual] | puts a character back into the input sequence, possibly modifying the input sequence (virtual protected member function of `std::basic_streambuf<CharT,Traits>`)

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