Library: Input/output
strstreambufbasic_streambuf
|
char_type freeze() int_type ios_type off_type |
overflow() pbackfail() pcount() pos_type seekoff() |
seekpos() setbuf() str() strstreambuf() traits_type |
underflow() xsputn() ~strstreambuf() |
Class that associates either the input sequence or the output sequence with a tiny character array whose elements store arbitrary values
#include <strstream>
namespace std {
class strstreambuf;
}
The class strstreambuf is derived from basic_streambuf specialized on type char to associate either the input sequence or the output sequence with a tiny character array whose elements store arbitrary values.
Each object of type strstreambuf controls two character sequences:
A character input sequence
A character output sequence
Note: see basic_streambuf.
The two sequences are related to each other, but are manipulated separately. This means that you can read and write characters at different positions in objects of type strstreambuf without any conflict (in opposition to the basic_filebuf objects).
The underlying array has several attributes:
allocated, set when a dynamic array has been allocated, and hence should be freed by the destructor of the strstreambuf object.
constant, set when the array has const elements, so the output sequence cannot be written.
dynamic, set when the array object is allocated (or reallocated) as necessary to hold a character sequence that can change in length.
frozen, set when the program has requested that the array not be altered, reallocated, or freed.
NOTE -- This is a deprecated feature and might not be available in future versions.
namespace std {
class strstreambuf
: public basic_streambuf<char> {
public:
typedef char_traits<char> traits_type;
typedef basic_ios<char, traits_type> ios_type;
typedef char char_type;
typedef typename traits_type::int_type int_type;
typedef typename traits_type::pos_type pos_type;
typedef typename traits_type::off_type off_type;
explicit strstreambuf(streamsize alsize = 0);
strstreambuf(void *(*palloc)(size_t),
void (*pfree)(void *));
strstreambuf(char *gnext, streamsize n, char *pbeg = 0);
strstreambuf(unsigned char *gnext, streamsize n,
unsigned char *pbeg = 0);
strstreambuf(signed char *gnext, streamsize n,
signed char *pbeg = 0);
strstreambuf(const char *gnext, streamsize n);
strstreambuf(const unsigned char *gnext, streamsize n);
strstreambuf(const signed char *gnext, streamsize n);
virtual ~strstreambuf();
void freeze(bool f = 1);
char *str();
int pcount() const;
protected:
virtual int_type overflow(int_type c = traits_type::eof());
virtual int_type pbackfail(int_type c = traits_type::eof());
virtual int_type underflow();
virtual pos_type seekoff(off_type, ios_type::seekdir way,
ios_type::openmode which =
ios_type::in | ios_type::out);
virtual pos_type seekpos(pos_type sp,
ios_type::openmode which =
ios_type::in | ios_type::out);
virtual streambuf* setbuf(char *s, streamsize n);
virtual streamsize xsputn(const char_type* s,
streamsize n);
};
}
char_type
The type char_type is a synonym of type char.
int_type
The type int_type is a synonym of type traits_type::in_type.
ios_type
The type ios_type is an instantiation of class basic_ios on type char.
off_type
The type off_type is a synonym of type traits_type::off_type.
pos_type
The type pos_type is a synonym of type traits_type::pos_type.
traits_type
The type traits_type is a synonym of type char_traits<char>.
explicit strstreambuf(streamsize alsize = 0);
Constructs an object of class strstreambuf, initializing the base class with streambuf(). After initialization the strstreambuf object is in dynamic mode and its array object has a size of alsize.
strstreambuf(void* (*palloc)(size_t),
void (*pfree)(void*));
Constructs an object of class strstreambuf, initializing the base class with streambuf(). After initialization the strstreambuf object is in dynamic mode. The function used to allocate memory is pointed to by void* (*palloc)(size_t) and the one used to free memory is pointed to by void (*pfree)(void*).
strstreambuf(char* gnext, streamsize n,
char* pbeg = 0);
strstreambuf(signed char* gnext, streamsize n,
signed char* pbeg = 0);
strstreambuf(unsigned char* gnext, streamsize n,
unsigned char* pbeg = 0);
Constructs an object of class strstreambuf, initializing the base class with streambuf(). The argument gnext points to the first element of an array object whose number of elements is:
n, if n > 0 ::strlen(gnext), if n == 0 INT_MAX, if n < 0
If pbeg is a null pointer, sets only the input sequence to gnext. Otherwise, also sets the output sequence to pbeg.
strstreambuf(const char* gnext, streamsize n); strstreambuf(const signed char* gnext, streamsize n); strstreambuf(const unsigned char* gnext, streamsize n);
Constructs an object of class strstreambuf, initializing the base class with streambuf(). The argument gnext points to the first element of an array object whose number of elements is:
n, if n > 0 ::strlen(gnext), if n == 0 INT_MAX, if n < 0
Sets the input sequence to gnext and the mode to constant.
virtual ~strstreambuf();
Destroys an object of class strstreambuf. The function frees the dynamically allocated array object only if allocated is set and frozen is not set.
void freeze(bool freezefl = true);
If both strmode and dynamic are non-zero, alters the freeze status of the dynamic array object as follows:
If freezefl is true, the function sets frozen in strmode.
Otherwise, it clears frozen in strmode.
int_type overflow( int_type c = traits_type::eof() );
If the output sequence has a put position available, and c is not traits_type::eof(), then writes c into it. If there is no position available, the function increases the size of the array object by allocating more memory, and then writes c at the new current put position. If dynamic is not set or if frozen is set, the operation fails. The function returns traits_type::not_eof(c), except if it fails, in which case it returns traits_type::eof().
int_type pbackfail( int_type c = traits_type::eof() );
Puts back the character designated by c into the input sequence. If traits_type::eq_int_type(c,traits_type::eof()) returns true, move the input sequence one position backward. If the operation fails, the function returns traits_type::eof(). Otherwise it returns traits_type::not_eof(c).
int pcount() const;
Returns the size of the output sequence.
pos_type
seekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which =
ios_base::in | ios_base::out);
If the open mode is in | out, alters the stream position of both the input and the output sequence. If the open mode is in, alters the stream position of only the input sequence. If the open mode is out, alters the stream position of only the output sequence. The new position is calculated by combining the two parameters off (displacement) and way (reference point). If the current position of the sequence is invalid before repositioning, the operation fails and the return value is pos_type(off_type(-1)). Otherwise the function returns the current new position.
pos_type
seekpos(pos_type sp, ios_base::openmode which =
ios_base::in | ios_base::out);
If the open mode is in | out, alters the stream position of both the input and the output sequence. If the open mode is in, alters the stream position of only the input sequence. If the open mode is out, alters the stream position of only the output sequence. If the current position of the sequence is invalid before repositioning, the operation fails and the return value is pos_type(off_type(-1)). Otherwise the function returns the current new position.
strstreambuf* setbuf(char* s, streamsize n);
If dynamic is set and freeze is not, proceed as follows:
If s is not a null pointer and n is greater than the number of characters already in the current array, replaces it (copy its contents) by the array of size n pointed to by s.
char* str();
Calls freeze(), then returns the beginning pointer for the input sequence. Note that the pointer need not point to a NUL-terminated character string. To obtain such a string the caller must explicitly NUL-terminate it first, for instance by inserting the std::ends manipulator into the stream.
int_type underflow();
If the input sequence has a read position available, returns the content of this position. Otherwise tries to expand the input sequence to match the output sequence and if possible returns the content of the new current position. The function returns traits_type::eof() to indicate failure.
In the case where s is a null pointer and n is greater than the number of characters already in the current array, resizes it to size n.
If the function fails, it returns a null pointer.
streamsize xsputn(const char_type* s, streamsize n);
Writes up to n characters to the output sequence. The characters written are obtained from successive elements of the array whose first element is designated by s. The function returns the number of characters written.
//
// strstreambuf.cpp
//
#include <iomanip> // for setw
#include <ios> // for dec, ends
#include <iostream> // for cerr, cout
#include <strstream> // for istream, ostrstream
int main ()
{
// create a write-only stream object
std::ostrstream out;
// tie the istream object to the ostrstream object
std::istream in (out.rdbuf ());
// output to out
out << "Anticonstitutionnellement is a big word!!!\n";
// create a NTBS
const char s[] ="Le rat des villes et le rat des champs.";
// output the NTBS
out << s << '\n';
// (try to) resize the buffer
if (out.rdbuf ()->pubsetbuf (0, 128L))
std::cout << "Successfully allocated buffer.\n";
else
std::cerr << "Failed to allocate buffer.\n";
// output the contents of the buffer to standard output
std::cout << in.rdbuf ();
// format a number into out
out << std::dec // decimal base
<< std::setfill ('#') // set fill character
<< std::setw (16) // set field width
<< 0x100 << '\n'; // format
// output the content of the input sequence to standard output
std::cout << in.rdbuf( ) << '\n';
// number of elements in the output sequence
const std::streamsize pcount = std::streamsize (out.rdbuf ()->pcount ());
std::cout << "Buffer size is " << pcount << '\n';
// (try to) resize the buffer
if (out.rdbuf ()->pubsetbuf (0, pcount * 2L))
std::cout << "\nSuccessfully resized buffer to " << pcount * 2 << '\n';
else
std::cerr << "\nFailed to resize buffer to " << pcount * 2 << '\n';
// NUL-terminate the character array before streaming it out
out << std::ends;
// output the contents of the streambuf object associated with out
std::cout << out.rdbuf ()->str ();
// unfreeze the streambuf so it cleans up its allocated memory
out.rdbuf ()->freeze (false);
return 0;
}
Program Output:
Successfully allocated buffer. Anticonstitutionnellement is a big word!!! Le rat des villes et le rat des champs. #############256 Buffer size is 100 Successfully resized buffer to 200 Anticonstitutionnellement is a big word!!! Le rat des villes et le rat des champs. #############256
char_traits, ios_base, basic_ios, basic_streambuf, istrstream, ostrstream, strstream
Deprecated. See ISO/IEC 14882:1998 -- International Standard for Information Systems --Programming Language C++, Annex D Compatibility features Section D.7.1