C#

System.IO.StreamReader sr = new System.IO.StreamReader("C:\\TargetFile.txt");

int b = sr.BaseStream.ReadByte();

while(b != -1)
{
char c = (char)b;

if(c != '0' && c != '1')
//DO ERROR HANDLING HERE

b = sr.BaseStream.ReadByte();
}

sr.Close();

//----------------------------------------------------------------------------------
// Count non-printable characters
// accepts printable characters, plus CR, LF and HTAB
// plus everything in accept string
// return false iff file contains too many non-printable characters
// UTF-8 files (starting with 0xEFBBBF) are always assumed printable.
// Unicode files (starting with 0xFFFE or 0xFEFF) are always assumed printable.
//----------------------------------------------------------------------------------
public static bool IsPrintableFile(string filename, byte[] accept, out long nonPrintables) {
	bool printable=true;
	bool firstRead=true;
	long chars=0;
	int logged=0;
	nonPrintables=0;
	if (accept==null) accept=new byte[0];
	using (LP_File f=new LP_File(filename)) {
		try {
			f.OpenBinaryReader();
			byte[] buffer=new byte[512];
			for ( ; ; ) {
				int len=f.ReadBinary(buffer);
				if (len<=0) break;
				if (firstRead) {
					firstRead=false;
					if (len>=2) {
						byte c0=buffer[0];
						byte c1=buffer[1];
						if (c0==0xFF && c1==0xFE) return true;
						if (c0==0xFE && c1==0xFF) return true;
						if (len>=3) {
							byte c2=buffer[2];
							if (c0==0xEF && c1==0xBB && c2==0xBF) return true;
						}
					}
				}
				for (int j=0 ; j< len ; j++) {
					byte c=buffer[j];
					chars++;
					if (c>=0x20 && c<=0x7F) continue;
					if (c=='\t' || c==0x0A || c==0x0D) continue;
					bool acceptable=false;
					for (int i=0 ; i< accept.Length ; i++) {
						if (c==accept[i]) acceptable=true;
					}
					if (!acceptable) {
						logged++;
						if (logged<20) {
							int i=(int)c;
							Console.WriteLine("Bad character ("+i.ToString("X2")+
								") in "+filename);
						}
						nonPrintables++;
					}
				}
			}
			f.CloseBinaryReader();
			if (logged!=0) Console.WriteLine(logged+" bad chars");
		} catch (Exception exc) {
			env.error("IO error on "+filename+": "+exc);
		}
	}
	if (nonPrintables>(chars/64)) printable=false;
	return printable;
}