If 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 |
|n||-|| the number of |
 Return value
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.
Provides a 10k buffer for reading. On linux, the strace utility may be used to observe the actual number of bytes read.
 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 173||C++98||the type of n was misspecified as int||corrected to std::streamsize|
 See also
| invokes setbuf() |
(public member function of
| sets the buffer and its size for a file stream |