char* getMemoBuf(int fieldno, int *len);

The function getMemoBuf() returns content of memo field or NULL.
It can requrn binary data too.
The library reuses memory for reading memo. You have to copy received data somewhere because they will be released at next call.
Do not forget to call readRecord().

{
    // your code
    dbf->readRecord( row );
    int len = 0;
    char *memo = dbf->getMemoBuf(0, &len);
    if (len)
        printf( "Length of memo = %d\n", len );
    // your code
}