s is a null pointer and
n is zero, the filebuf becomes unbuffered for output, meaning
pptr() are null and any output is immediately sent to file.
Otherwise, a call to
setbuf() replaces the internal buffer (the controlled character sequence) with the user-supplied character array whose first element is pointed to by
s and allows this std::basic_filebuf object to use up to
n bytes in that array for buffering.
This function is protected virtual, it may only be called through
pubsetbuf() or from member functions of a user-defined class derived from
|s||-||pointer to the first byte in the user-provided buffer or null|
|n||-||the number of bytes in the user-provided buffer or zero|
*this, cast to the base class
The conditions when this function may be used and the way in which the provided buffer is used is implementation-defined.
- GCC 4.6 libstdc++
setbuf()may only be called when the std::basic_filebuf is not associated with a file (has no effect otherwise). With a user-provided buffer, reading from file reads
n-1bytes at a time.
- Clang++3.0 libc++
setbuf()may be called after opening the file, but before any I/O (may crash otherwise). With a user-provided buffer, reading from file reads largest multiples of 4096 that fit in the buffer.
- Visual Studio 2010
setbuf()may be called at any time, even after some I/O took place. Current contents of the buffer, if any, are lost.
The standard does not define any behavior for this function except that
setbuf(0, 0) called before any I/O has taken place is required to set unbuffered output.
provide a 10k buffer for reading. On linux, the strace utility may be used to observe the actual number of bytes read