Getting the size of a micro SD card via C++

Question

I am looking for some function that will return the total capacity of a micro SD card mounted to /dev/sdb. I do not care so much about free space I care about total capacity of the drive. I need a reliable and accurate function. If there is none in existence how would I go about creating one?

Thanks!

Answer 1

strace for blockdev tells me you could use:

#include <iostream>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#include <sys/ioctl.h>
#include <linux/fs.h>

int main()
{
    unsigned long long size;
    int fd = open("/dev/sdx", O_RDONLY);
    ioctl(fd, BLKGETSIZE64, &size);

    std::cout << size << std::endl;
    std::cout << (size>>20) << std::endl; // MiBytes
}

(replace sdx by device node name)

Note prefer using uint64_t if your compiler supports it already (include <cstdint>)

Answer 2

You can just read a special file in the /sys/ directory:

/sys/block/sdb/sdb1/size

It returns the size in bytes.