std::basic_streambuf<CharT,Traits>::pubsetbuf, std::basic_streambuf<CharT,Traits>::setbuf

 

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std::basic_streambuf

Public member functions basic_streambuf::~basic_streambuf      Locales basic_streambuf::pubimbue basic_streambuf::getloc Positioning basic_streambuf::pubsetbuf basic_streambuf::pubseekoff basic_streambuf::pubseekpos basic_streambuf::pubsync Get area basic_streambuf::in_avail basic_streambuf::snextc basic_streambuf::sbumpc basic_streambuf::sgetc basic_streambuf::sgetn Put area basic_streambuf::sputc basic_streambuf::sputn Putback basic_streambuf::sputbackc basic_streambuf::sungetc

Protected member functions basic_streambuf::basic_streambuf basic_streambuf::operator= (C++11) basic_streambuf::swap (C++11) Locales basic_streambuf::imbue Positioning basic_streambuf::setbuf basic_streambuf::seekoff basic_streambuf::seekpos basic_streambuf::sync Get area basic_streambuf::showmanyc basic_streambuf::underflow basic_streambuf::uflow basic_streambuf::xsgetn basic_streambuf::ebackbasic_streambuf::gptrbasic_streambuf::egptr basic_streambuf::gbump basic_streambuf::setg Put area basic_streambuf::xsputn basic_streambuf::overflow basic_streambuf::pbasebasic_streambuf::pptrbasic_streambuf::epptr basic_streambuf::pbump basic_streambuf::setp Putback basic_streambuf::pbackfail

 

public: basic_streambuf<CharT, Traits>* pubsetbuf( char_type* s, std::streamsize n )	(1)
protected: virtual basic_streambuf<CharT, Traits>* setbuf( char_type* s, std::streamsize n )	(2)

1) Calls setbuf(s, n) of the most derived class.

2) The base class version of this function has no effect. The derived classes may override this function to allow removal or replacement of the controlled character sequence (the buffer) with a user-provided array, or for any other implementation-specific purpose.

Parameters

s	-	pointer to the first CharT in the user-provided buffer
n	-	the number of CharT elements in the user-provided buffer

Return value

1) The return value of setbuf(s, n).

2) this

Example

Provides a 10k buffer for reading. On linux, the strace utility may be used to observe the actual number of bytes read.

Run this code

#include <fstream>
#include <iostream>
#include <string>

int main()
{
    int cnt = 0;
    std::ifstream file;
    char buf[1024 * 10 + 1];
    
    file.rdbuf()->pubsetbuf(buf, sizeof buf);
    
    file.open("/usr/share/dict/words");
    
    for (std::string line; getline(file, line);)
        ++cnt;
    
    std::cout << cnt << '\n';
}

Possible output:

356010

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 158	C++98	the default behavior of setbuf was only specified if gptr() is not null and not equal to egptr()	specified as no-op for all cases

See also

setbuf [virtual]	attempts to replace the controlled character sequence with an array (virtual protected member function of std::basic_stringbuf<CharT,Traits,Allocator>)
setbuf [virtual]	provides user-supplied buffer or turns this filebuf unbuffered (virtual protected member function of std::basic_filebuf<CharT,Traits>)
setbuf [virtual]	attempts to replace the controlled character sequence with an array (virtual protected member function of std::strstreambuf)
setbuf	sets the buffer for a file stream (function)