Read/Write a binary file
CAVEAT. This recipe was cooked in Linux and uses the file /dev/urandom which will be present in all Unix-like systems as far as the author knows. So, Linux, Mac, BSD are all fine.
Sometimes your file contains stuff which is not intended to be interpreted as a sequence of characters. This can be the case, for example, if you are reading/writing some compressed data, some audio file, a big matrix, a picture etc.
Reading from a binary file
Problem. I want to have a quite good random number and I know than most Unix systems provide a file /dev/urandom where I can read as many as I want. Please see your operating system documentation of the file to know how it works. This is a classic example of a binary stream, when I read from /dev/urandom I am supposed to read byte per byte, e.g. it would make not much sense to try to read a line. Also, this example is nice because you are not supposed to read in all the file, since this file has no end! You must read only a certain amount of it.
Solution. Follow the sequence of commands below to see how you can read from /dev/urandom as a binary stream.
"Make a ReadStream from a file" rs _ '/dev/urandom' asFileEntry readStream. rs class. "=> StandardFileStream " " generally you may want to read a binary stream as a sequence of bytes." rs useBytes . " get the fisrt byte" rs next. "=> 7 " "get the following 10 bytes" tmp _ rs next: 10. "=> #[192 101 93 30 46 183 55 186 231 66] " tmp class. "=> ByteArray " " get 'tmp' in hex format, spaces added for readability by hand " tmp hex. " 'EF F6 F0 1A 78 14 C0 02 73 1C' " " get 'tmp' as base64, will make it shorter " tmp base64Encoded . "=> '15vGaEu2IU1NAQ==' " " let's see what comes back if we read in binary mode" tmp2 _ rs next. "=> 238 " tmp2 class. "=> SmallInteger " " we may want to read the binary stream as characters " rs useCharacters . rs next: 10. "=> ')Orý»¯Ê³' " " when you finished remember to close the stream. " rs close.
TODO: Writing a binary file
To remember here is that writeStream asks confirmation if the file already exists, to have no question asked use forceWriteStream.
Dr. Nicola Mingotti last updated this on 3-Sep-2021. Examples where run in Cuis-5.0-4815.image.