http://kor.i2p/books/The%20C%20Programming%20Language%20by%20K&R/appb.html
For x or X , 0x or 0X will be prefixed to a non-zero result.
For e , E , f , g , and G ,
the output will always have a decimal point; for g and G , trailing zeros will not be removed. A number specifying a minimum field width.