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jlechner |
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From: kuehl@ramsen.informatik.uni-konstanz.de (Dietmar Kuehl)
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Newsgroups: comp.std.c++
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Subject: Re: binary iostreams ?
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Date: Sat, 3 Feb 2001 17:17:49 GMT
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Message-ID: <95hctq$suu$2@news.BelWue.DE>
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Hi,
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Plinio Conti (plinio.contiNO@SPAMMINGmclink.it) wrote:
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: Why std c++ library stream classes are only text-oriented?
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There is only a text oriented front end to stream buffers because text
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input and output does not vary between platforms. This is very
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different for binary output. For example, binary output has to consider
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- word sizes: Is an 'int' two, four, or eight bytes long? The same
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questions arise for all other built-in types.
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- what is the bit pattern of a value? I think that at least implicitly
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in the standard a binary representation for integer types is required.
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I don't think that it is required to use two's complement. In any
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case, the floating point representations do differ, eg. in their
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number of bytes used.
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- what "endianess" is to be used?
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Basically it is possible to decide a format for each of those. This,
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however, implies inefficient implementations on platforms where the
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format does not match the internal representation.
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What many people asking for binary I/O forget is that binary I/O also
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requires some form of formatting! Assuming that just writing data and
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then reading it in will work is asking for problems, eg. when the
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compiler version changes and they decided to use a 32 bit integer
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rather than a 16 bit integer: It is not even necessary to switch
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platforms to run into problems!
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: I mean, if I want to write an int, a float, etc. AS IT IS I can't use
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: streams, because they write and read a human readable text format of
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: numbers.
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Which is for most I/O a reasonable approach. If it is not for you, you
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might want to consider a data base: File I/O is not really useful as a
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persistance mechanism. It is fine eg. for user interaction (text I/O),
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logging (text I/O), cross platfrom program interaction (formatted I/O),
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and data exchange (formatted I/O). In all these cases, the I/O is
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formatted, although possible using a binary format. For persistance,
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data bases are used. Depending on your needs, a relational or an object
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oriented one may be better suited.
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That said, it is worth to mention that it is easy to create a hierarchy
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similar to IOStreams built on top of stream buffers but doing binary
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formatting. A somewhat aged example is found at
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.
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This uses XDR formatting of the binary data (well, if I remmeber
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correctly, it is easy to plug in a different binary formatting).
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: Does anyone know how to solve the problem?
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Use a data base, text formatting, or binary formatting. With the
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details you have given it is impossible to tell which of those is the
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right approach because you haven't told *why* you want a binary format
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and *what* you want to do. That basically means that you came up with
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solution and you want us to confirm that it is the right one without
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telling us what problem is solved! Until I have seen the problem I
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doubt that binary I/O is the right approach...
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... and, BTW, using 'std::istream::read()' and 'std::ostream::write()'
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is almost certainly the *wrong* approach! These functions are an
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historical mistake which should have been corrected in the standard:
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It is my understanding that these methods were present in the IOStream
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version predating the rework from Jerry Schwartz and were left in to
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be compatible with the earlier stuff although they were not necessary:
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You could get binary I/O from the stream buffer level. The original
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IOStream library (maybe you remember using ) did not have
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stream buffers and thus basic support for binary I/O was also present
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on the streams level.
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: What do you think about this choice?
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When I wrote the above paragraph about confirming your choice, I haven't
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read this question! As I said above: You told us what solution you have
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choosen without stating what problem is solved. We cannot determine
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whether your choice is the right one. Actually, I'm pretty sure it is
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the wrong one but without seen the details I can't be certain.
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--
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Phaidros eaSE - Easy Software Engineering:
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