I am writing a program in C using usb.h where ManufacturerID of USB is in __u16 format. How to print it using printf.If I use %d it gives Segmentation Fault as output and if I use %c it gives some weird symbol.Does it have some other format specifier?
What's the result of sizeof(__u16)? 2?
You should probably typecast it to unsigned int, and pass that to printf. Or possibly to unsigned short.
Since it's likely unsigned, use %u.
What I suspect is happening is that the compiler writers didn't bother to make __u16 undergo standard integer promotion, which is needed by printf. So you have to cast it to a standard C type.
Last edited by King Mir; 06-23-2011 at 10:53 PM.
It is too clear and so it is hard to see.
A dunce once searched for fire with a lighted lantern.
Had he known what fire was,
He could have cooked his rice much sooner.
" idVendor 0x%04x %s\n"
This is what I saw here:
Koders Code Search: lsusb.c - C - GPL
u16 means 16 bit unsigned char.As you mentioned it should return sizeof() as 2
It is far more likely that the %s also in the format string is trying to follow a junk pointer.
Run the code in the debugger, and start examining stack traces and variables to figure out where things crash.
Also, show us YOUR code as well, not just the example you're copying from.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
the %s prints the name of manufacturer in that code.I just printed using %04x and got the right o/p.%u doesn't work here,gives the wrong ID.Anyway,got it solved thanks.%04x gives hexadecimal o/p
If %d causes a segfault, then changing %x won't fix it. You haven't fixed that problem. You still have a bug somewhere.
It is too clear and so it is hard to see.
A dunce once searched for fire with a lighted lantern.
Had he known what fire was,
He could have cooked his rice much sooner.
Is this not defined in their header? ... Have you looked? (Headers are text files, you can view them in notepad...)Originally Posted by jaypatel
I'm guessing (and it is only a guess) that it's an unsigned short int ... In which case "%hd" should print it correctly.
