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

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.

#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';
}

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

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

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