MeterFilter

From Crypto++ Wiki

A MeterFilter counts the number of bytes processed by the filter. The sample below demonstrates use of a Redirector and MeterFilter to count the number of bytes output by the HexEncoder and subsequently input to the StringSink.

byte data[] = { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07 };

string encoded;
MeterFilter meter( new StringSink( encoded ) );

ArraySource( data, sizeof( data ), true,
    new HexEncoder(
        new Redirector( meter ),
        true /*UCase*/, 2 /*Group*/,
        " " /*Separator*/
    )
);

cout << "processed " << meter.GetTotalBytes() << " bytes" << endl;
cout << encoded << endl;

Output: Processed 23 bytes
00 01 02 03 04 05 06 07