[erlang-questions] read_file -- binary data object

[by]

This can be achieved by pattern matching.

Like
<<A:1,B:1,C>> = Bin.
A B C stores the specified data with type integer(character)

Yao

> 在 2018年12月20日，08:04，Donald Steven <t6sn7gt@REDACTED> 写道：
> 
> Thanks Craig.  I don't think I expressed my question well.
> 
> Taking your foo1,txt example, when I read it back (file:read_file("foo1.txt"), how do I access the individual characters of "Something I'll write to disk."  That is, if file:read_file("foo1.txt") yields {ok,<<"Something I'll write to disk.">>}, how do I read the "S", then the "o", etc.?
> 
> Don
> 
>> On 12/19/2018 6.48 PM, zxq9@REDACTED wrote:
>>> On 2018年12月19日水曜日 18時40分05秒 JST Donald Steven wrote:
>>> The manual for the function read_file/1 says: Returns {ok, Binary}, where Binary is a binary data object that contains the contents of Filename, or {error, Reason} if an error occurs.
>>> 
>>> What is the type of this "binary data object" (a list?).  (I'll want to access individual elements.)
>> It is an Erlang binary.
>> 
>> 
>> 1> Foo1 = "Something I'll write to disk.".
>> "Something I'll write to disk."
>> 2> Foo2 = <<"Something else I'll write to disk.">>.
>> <<"Something else I'll write to disk.">>
>> 3> Foo3 = <<1,2,3,4>>.
>> <<1,2,3,4>>
>> 4> file:write_file("foo1.txt", Foo1).
>> ok
>> 5> file:write_file("foo2.txt", Foo2).
>> ok
>> 6> file:write_file("foo3", Foo3).
>> ok
>> 7> file:read_file("foo1.txt").
>> {ok,<<"Something I'll write to disk.">>}
>> 8> file:read_file("foo2.txt").
>> {ok,<<"Something else I'll write to disk.">>}
>> 9> file:read_file("foo3").
>> {ok,<<1,2,3,4>>}
>> 
>> 
>> If the above seems perplexing then check out the docs on Erlang binaries.
>> They are awesome, especially when dealing with binary file formats or network data.
>> 
>> http://erlang.org/doc/reference_manual/expressions.html#bit_syntax
>> http://erlang.org/doc/programming_examples/bit_syntax.html
>> http://erlang.org/doc/man/binary.html
>> 
>> Also, keep in mind that "object" is a heavily overloaded term in computing.
>> The docs mean "returns a self-contained thingy that can be labeled and carries
>> a type (binary) native to the runtime".
>> 
>> -Craig
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