Linux - Reading File from Sudo - "Permission Denied" - c++

Question

When performing a recursive directory scan of the drive to generate a hash for each file by running the program executable under sudo, I'm discovering 1,000s of files are throwing "Permission Denied" errors.
My Question: Is this by design, why is sudo unable to read the files? Is what I'm doing even possible because files might be encrypted or currently in use during the time of the scan?
When I compile to Mac OSX and perform the same scan under sudo, I don't have this issue, just Linux.
Distro: 3.19.0-25-generic #26~14.04.1-Ubuntu SMP Fri Jul 24 21:16:20 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
An example of files with permission denied:
Can't open file: "/sys/class/gpio/unexport"
MSG: "Permission denied"
Can't open file: "/sys/class/gpio/export"
MSG: "Permission denied"
Sample of permission settings:
/sys/class/gpio$ ls -al
total 0
drwxr-xr-x 2 root root 0 Oct 5 04:51 .
drwxr-xr-x 57 root root 0 Oct 4 11:25 ..
--w------- 1 root root 4096 Oct 5 04:51 export
--w------- 1 root root 4096 Oct 5 04:51 unexport
MD5 Function where file reads fail:
QByteArray MD5(QString sPath)
{
QByteArray resultMD5 = NULL;
QFile* file = new QFile(sPath);
if(file->open(QIODevice::ReadOnly))
{
QCryptographicHash* pHashMD5 = NULL;
resultMD5 = pHashMD5->hash(file->readAll(),QCryptographicHash::Md5);
file->close();
//Clean up pointer
delete pHashMD5;
delete file;
}
else
{
qDebug() << "Can't open file: " << sPath;
qDebug() << "MSG: " << file->errorString();
file->close();
delete file;
}
return resultMD5;
}

Answer 1

What is under /sys are not really files. It's an interface into the kernel.
With regard to the examples you have mentioned, see here for an explanation of what they do.
Given their function, it makes no sense to consider that such "files" could be read.