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