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

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< cpp‎ | io‎ | basic streambuf

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';
    }

### 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)

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