Reading an sd card id in c

knobby67 · 02-27-2018, 06:06 AM

Hi All,
can anyone show me how to read the CID from a sd card in c(++) code? I've searched and found how to using cat /sys/block/mmcblk0/device/cid but can't find anyway in C. I could use system but don't know how I'd get the id numbers from that.
Thanks for the advise.

rtmistler · 02-27-2018, 06:33 AM

From within your program will you know the file to access all the time? Because you can use open() or fopen() from within the C program to open any file on the system, and then read from it. What I typically find is that I have to also do some in program research to find the correct file, because you can have stuff like /dev/sda1, or /dev/sdb2, and so forth and you want the correct reference file.

knobby67 · 02-27-2018, 08:03 AM

Thanks but I'm unsure how I can read the CID from that?

rtmistler · 02-27-2018, 08:13 AM

What exactly do you not understand? How to open a file and read it using C?

rknichols · 02-27-2018, 08:17 AM

Quote:

Originally Posted by knobby67

I've searched and found how to using cat /sys/block/mmcblk0/device/cid but can't find anyway in C.

Since you appear to know the file name, you can open that file in C with open() or fopen() just as you could any other file.

sundialsvcs · 02-28-2018, 09:09 AM

Quote:

Originally Posted by rknichols

Since you appear to know the file name, you can open that file in C with open() or fopen() just as you could any other file.

And that would be "the way to do it in Linux."

All of these so-called "pseudo file-systems" are, in fact, a kernel API. This is the (only) way that the kernel presents this information to you. When you "open and read from" one of these "files" – and/or in some cases "write to" them – you are communicating with a kernel interface that is presenting data to you in text form.

knobby67 · 02-28-2018, 09:31 AM

Thanks All. Thought I could use open.