I'm asking about %Id, not %ld.
Can anyone please explain to me what does "I" exactly do:
IFor decimal integer conversion (i,d,u) the output uses the locale's alternative output digits, if any. For example, since glibc 2.2.3 this will give Arabic-Indic digits in the Persian ("fa_IR") locale.
As an example:
printf("%Id",1);
In other words what is the difference between %d and %Id ?
can anyone please explain it with simple words and simple example stating the difference ?
printf format option I is a glibC extension to select a locale representation for numbers. It is not defined by the C Standard and should not be used in portable code.
If the locale is properly selected and supported by your C library, calling printf("%Id", 1); might produce a string encoding the Unicode code point U+0661 ١ that is the representation of the digit one in arabic.
See http://www.fileformat.info/info/unicode/char/0661/index.htm
Conversely, printf("%d", 1); always prints 1, the western representation of number one.
To make matters even more confusing, 1 is called an arabic numeral, as opposed to roman numeral I... unrelated to the I in %Id.