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basic_stringbuf Class

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The latest version of this topic can be found at basic_stringbuf Class.

Describes a stream buffer that controls the transmission of elements of type Elem, whose character traits are determined by the class Tr, to and from a sequence of elements stored in an array object.

Syntax

template <class Elem, class Tr = char_traits<Elem>,   
    class Alloc = allocator<Elem>>  
class basic_stringbuf : public basic_streambuf<Elem, Tr>

Parameters

Alloc
The allocator class.

Elem
The type of the basic element of the string.

Tr
The character traits specialized on the basic element of the string.

Remarks

The object is allocated, extended, and freed as necessary to accommodate changes in the sequence.

An object of class basic_stringbuf< Elem, Tr, Alloc> stores a copy of the ios_base::openmode argument from its constructor as its stringbuf mode mode:

  • If mode & ios_base::in is nonzero, the input buffer is accessible. For more information, see basic_streambuf Class.

  • If mode & ios_base::out is nonzero, the output buffer is accessible.

Constructors

basic_stringbuf Constructs an object of type basic_stringbuf.

Typedefs

allocator_type The type is a synonym for the template parameter Alloc.
char_type Associates a type name with the Elem template parameter.
int_type Makes this type within basic_filebuf's scope equivalent to the type of the same name in the Tr scope.
off_type Makes this type within basic_filebuf's scope equivalent to the type of the same name in the Tr scope.
pos_type Makes this type within basic_filebuf's scope equivalent to the type of the same name in the Tr scope.
traits_type Associates a type name with the Tr template parameter.

Member Functions

overflow A protected, virtual function that can be called when a new character is inserted into a full buffer.
pbackfail The protected virtual member function tries to put back an element into the input buffer, then makes it the current element (pointed to by the next pointer).
seekoff The protected virtual member function tries to alter the current positions for the controlled streams.
seekpos The protected virtual member function tries to alter the current positions for the controlled streams.
str Sets or gets the text in a string buffer without changing the write position.
swap
underflow The protected virtual member function to extract the current element from the input stream.

Requirements

Header: <sstream>

Namespace: std

basic_stringbuf::allocator_type

The type is a synonym for the template parameter Alloc.

typedef Alloc allocator_type;

basic_stringbuf::basic_stringbuf

Constructs an object of type basic_stringbuf.

basic_stringbuf(
    ios_base::openmode _Mode = ios_base::in | ios_base::out);

basic_stringbuf(
    const basic_string<Elem, Tr, Alloc>& str,  
    ios_base::openmode _Mode = ios_base::in | ios_base::out);

Parameters

_Mode
One of the enumerations in ios_base::openmode.

str
An object of type basic_string.

Remarks

The first constructor stores a null pointer in all the pointers controlling the input buffer and the output buffer. For more information, see the Remarks section of the basic_streambuf Class. It also stores _Mode as the stringbuf mode. For more information, see the Remarks section of the basic_stringbuf Class.

The second constructor allocates a copy of the sequence controlled by the string object str. If _Mode & ios_base::in is nonzero, it sets the input buffer to start reading at the start of the sequence. If _Mode & ios_base::out is nonzero, it sets the output buffer to begin writing at the start of the sequence. It also stores _Mode as the stringbuf mode. For more information, see the Remarks section of the basic_stringbuf Class.

basic_stringbuf::char_type

Associates a type name with the Elem template parameter.

typedef Elem char_type;

basic_stringbuf::int_type

Makes this type within basic_filebuf's scope equivalent to the type of the same name in the Tr scope.

typedef typename traits_type::int_type int_type;

basic_stringbuf::off_type

Makes this type within basic_filebuf's scope equivalent to the type of the same name in the Tr scope.

typedef typename traits_type::off_type off_type;

basic_stringbuf::overflow

A protected virtual function that can be called when a new character is inserted into a full buffer.

virtual int_type overflow(int_type _Meta = traits_type::eof());

Parameters

_Meta
The character to insert into the buffer, or traits_type::eof.

Return Value

If the function cannot succeed, it returns traits_type::eof. Otherwise, it returns traits_type::not_eof(_ Meta).

Remarks

If _ Meta does not compare equal to traits_type::eof, the protected virtual member function tries to insert the element traits_type::to_char_type(_ Meta) into the output buffer. It can do so in various ways:

  • If a write position is available, it can store the element into the write position and increment the next pointer for the output buffer.

  • It can make a write position available by allocating new or additional storage for the output buffer. Extending the output buffer this way also extends any associated input buffer.

basic_stringbuf::pbackfail

The protected virtual member function tries to put back an element into the input buffer, and then make it the current element (pointed to by the next pointer).

virtual int_type pbackfail(int_type _Meta = traits_type::eof());

Parameters

_Meta
The character to insert into the buffer, or traits_type::eof.

Return Value

If the function cannot succeed, it returns traits_type::eof. Otherwise, it returns traits_type::not_eof(_ Meta).

Remarks

If _Meta compares equal to traits_type::eof, the element to push back is effectively the one already in the stream before the current element. Otherwise, that element is replaced by byte = traits_type::to_char_type(_ Meta). The function can put back an element in various ways:

  • If a putback position is available, and the element stored there compares equal to byte, it can decrement the next pointer for the input buffer.

  • If a putback position is available, and if the stringbuf mode permits the sequence to be altered ( mode & ios_base::out is nonzero), it can store byte into the putback position and decrement the next pointer for the input buffer.

basic_stringbuf::pos_type

Makes this type within basic_filebuf's scope equivalent to the type of the same name in the Tr scope.

typedef typename traits_type::pos_type pos_type;

basic_stringbuf::seekoff

The protected virtual member function tries to alter the current positions for the controlled streams.

virtual pos_type seekoff(
    off_type _Off,  
    ios_base::seekdir _Way,  
    ios_base::openmode _Mode = ios_base::in | ios_base::out);

Parameters

_Off
The position to seek for relative to _Way. For more information, see basic_stringbuf::off_type.

_Way
The starting point for offset operations. See ios_base::seekdir for possible values.

_Mode
Specifies the mode for the pointer position. The default is to allow you to modify the read and write positions. For more information, see ios_base::openmode.

Return Value

Returns the new position or an invalid stream position.

Remarks

For an object of class basic_stringbuf<Elem, Tr, Alloc>, a stream position consists purely of a stream offset. Offset zero designates the first element of the controlled sequence.

The new position is determined as follows:

  • If _Way == ios_base::beg, the new position is the beginning of the stream plus _Off.

  • If _Way == ios_base::cur, the new position is the current stream position plus _Off.

  • If _Way == ios_base::end, the new position is the end of the stream plus _Off.

If _Mode & ios_base::in is nonzero, the function alters the next position to read in the input buffer. If _Mode & ios_base::out is nonzero, the function alters the next position to write in the output buffer. For a stream to be affected, its buffer must exist. For a positioning operation to succeed, the resulting stream position must lie within the controlled sequence. If the function affects both stream positions, _Way must be ios_base::beg or ios_base::end and both streams are positioned at the same element. Otherwise (or if neither position is affected), the positioning operation fails.

If the function succeeds in altering either or both of the stream positions, it returns the resultant stream position. Otherwise, it fails and returns an invalid stream position.

basic_stringbuf::seekpos

The protected virtual member function tries to alter the current positions for the controlled streams.

virtual pos_type seekpos(pos_type _Sp, ios_base::openmode _Mode = ios_base::in | ios_base::out);

Parameters

_Sp
The position to seek for.

_Mode
Specifies the mode for the pointer position. The default is to allow you to modify the read and write positions.

Return Value

If the function succeeds in altering either or both of the stream positions, it returns the resultant stream position. Otherwise, it fails and returns an invalid stream position. To determine if the stream position is invalid, compare the return value with pos_type(off_type(-1)).

Remarks

For an object of class basic_stringbuf< Elem, Tr, Alloc>, a stream position consists purely of a stream offset. Offset zero designates the first element of the controlled sequence. The new position is determined by _ Sp.

If mode & ios_base::in is nonzero, the function alters the next position to read in the input buffer. If mode & ios_base::out is nonzero, the function alters the next position to write in the output buffer. For a stream to be affected, its buffer must exist. For a positioning operation to succeed, the resulting stream position must lie within the controlled sequence. Otherwise (or if neither position is affected), the positioning operation fails.

basic_stringbuf::str

Sets or gets the text in a string buffer without changing the write position.

basic_string<Elem, Tr, Alloc> str() const;
  
void str(
    const basic_string<Elem, Tr, Alloc>& _Newstr);

Parameters

_Newstr
The new string.

Return Value

Returns an object of class basic_string< Elem, Tr, Alloc >, whose controlled sequence is a copy of the sequence controlled by *this.

Remarks

The first member function returns an object of class basic_string< Elem, Tr, Alloc>, whose controlled sequence is a copy of the sequence controlled by *this. The sequence copied depends on the stored stringbuf mode:

  • If mode & ios_base::out is nonzero and an output buffer exists, the sequence is the entire output buffer ( epptr - pbase elements beginning with pbase).

  • If mode & ios_base::in is nonzero and an input buffer exists, the sequence is the entire input buffer ( egptr - eback elements beginning with eback).

  • Otherwise, the copied sequence is empty.

The second member function deallocates any sequence currently controlled by *this. It then allocates a copy of the sequence controlled by _Newstr. If mode & ios_base::in is nonzero, it sets the input buffer to start reading at the beginning of the sequence. If mode & ios_base::out is nonzero, it sets the output buffer to start writing at the beginning of the sequence.

Example

// basic_stringbuf_str.cpp  
// compile with: /EHsc  
#include <iostream>  
#include <sstream>  
  
using namespace std;  
  
int main( )   
{  
   basic_string<char> i( "test" );  
   stringstream ss;  
  
   ss.rdbuf( )->str( i );  
   cout << ss.str( ) << endl;  
  
   ss << "z";  
   cout << ss.str( ) << endl;  
  
   ss.rdbuf( )->str( "be" );  
   cout << ss.str( ) << endl;  
}  

test  
zest  
be

basic_stringbuf::traits_type

Associates a type name with the Tr template parameter.

typedef Tr traits_type;

Remarks

The type is a synonym for the template parameter Tr.

basic_stringbuf::underflow

Protected, virtual function to extract the current element from the input stream.

virtual int_type underflow();

Return Value

If the function cannot succeed, it returns traits_type::eof. Otherwise, it returns the current element in the input stream, which are converted.

Remarks

The protected virtual member function tries to extract the current element byte from the input buffer, advance the current stream position, and return the element as traits_type::to_int_type( byte). It can do so in one way: If a read position is available, it takes byte as the element stored in the read position and advances the next pointer for the input buffer.

basic_streambuf::swap

Swaps the contents of this string buffer with another string buffer.

void basic_stringbuf<T>::swap
(basic_stringbuf& other)

Parameters

other
The basic_stringbuf whose contents will be swapped with this basic_stringbuf.

Remarks

basic_stringbuf::operator=

Assigns the contents of the basic_stringbuf on the right side of the operator to the basic_stringbuf on the left side..

basic_stringbuf& basic_stringbuf:: operator=(const basic_stringbuf& other)

Parameters

other
A basic_stringbuf whose contents, including locale traits, will be assigned to the stringbuf on the left side of the operator.

Remarks

See Also

Thread Safety in the C++ Standard Library
iostream Programming
iostreams Conventions