Name  

Meaning  

_IOFBF  

The file is fully buffered. When a buffer is empty, the next input operation will attempt to fill the entire buffer.  

 

On output, the buffer will be completely filled before any data is written to the file.  

_IOLBF  

The file is line buffered. When a buffer is empty, the next input operation will still attempt to fill the entire buffer.  

 

On output, however, the buffer will be flushed whenever a newline character is written to the file.  

_IONBF  

The file is unbuffered. The buf and size parameters of setbuf are ignored. Each input operation will read directly from the file, and each output operation will immediately write the data to the file.