# std::basic_stringbuf<CharT,Traits,Allocator>::setbuf

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< cpp‎ | io‎ | basic stringbuf

protected: virtual std::basic_streambuf <CharT, Traits>* setbuf( char_type* s, std::streamsize n ) |  |

If `s` is a null pointer and `n` is zero, this function has no effect.

Otherwise, the effect is implementation-defined: some implementations do nothing, while some implementations clear the std::string member currently used as the buffer and begin using the user-supplied character array of size `n`, whose first element is pointed to by `s`, as the buffer and the input/output character sequence.

This function is protected virtual, it may only be called through `pubsetbuf()` or from member functions of a user-defined class derived from `std::basic_stringbuf`.

### Parameters

s | - | pointer to the first CharT in the user-provided buffer or null
n | - | the number of CharT elements in the user-provided buffer or zero

### Return value

this.

### Notes

The deprecated stream buffer std::strstreambuf or the boost.IOStreams device `boost::basic_array` may be used to implement I/O buffering over a user-provided char array in portable manner.

### Example

Test for the stringstream's setbuf functionality

Run this code

    #include <iostream>
    #include <sstream>

    int main()
    {
        std::ostringstream ss;
        char c[1024] = {};
        ss.rdbuf()->pubsetbuf(c, 1024);
        ss << 3.14 << '\n';
        std::cout << c << '\n';
    }

Output:

    3.14 (on GNU g++/libstdc++ and SunPro C++/roguewave)
    <nothing> (on MS Visual Studio 2010, SunPro C++/stlport4, CLang++/libc++)

### See also

pubsetbuf | invokes setbuf() (public member function of `std::basic_streambuf<CharT,Traits>`)

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