Question

int x; printf('hello %n World\n', &x); printf('%d\n', x); 

Answer 1

It’s not so useful for printf(), but it can be very useful for sscanf(), especially if you’re parsing a string in multiple iterations. fscanf() and scanf() automatically advance their internal pointers by the amount of input read, but sscanf() does not. For example:

char stringToParse[256]; ... char *curPosInString = stringToParse;  // start parsing at the beginning int bytesRead; while(needsParsing()) {     sscanf(curPosInString, '(format string)%n', ..., &bytesRead);  // check the return value here     curPosInString += bytesRead;  // Advance read pointer     ... }