how to use c get size of a file which is created using dd command

Question

i create a file using dd command like this:

dd if=/dev/zero of=1g.dd bs=1M count=512 seek=512

when i run command ls 1g.dd, its size is 1G, run du 1g.dd, it's 512M.

there is a struct stat in c library to read file size, but it can only read out that 1G size, now how can i get that 512M size which is the real size of that file?

now the only way i know is to parse shell command du's output. can i read out the size from the file directly?

Answer 1

You can use the st_blocks member of struct stat for that, it tells you how many 512 byte blocks (this is valid on Linux, could be different on other OSes, and could depend on the filesystem) have been allocated to the file.