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https://issues.apache.org/jira/browse/AVRO-1216?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15307801#comment-15307801
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John McClean commented on AVRO-1216:
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[~thiru_mg]: can you take a look at this patch when you get a chance?
> Setting precision for the output stream
> ---------------------------------------
>
> Key: AVRO-1216
> URL: https://issues.apache.org/jira/browse/AVRO-1216
> Project: Avro
> Issue Type: Bug
> Components: c++
> Affects Versions: 1.7.2
> Environment: Linux x86_64
> Reporter: Paul Jacobs
> Assignee: John McClean
> Attachments: AVRO-1216.patch, cpx.json, precision.cpp
>
>
> There's no way, that I know of, to set the precision level on the output
> stream.
> I want to take an avro object, with double fields, and json encode it into a
> string. However, when I do this the encoded doubles have lost precision. I
> suspect this is because the precision I set on the ostringstream and
> resulting avro::ostreamOutputStream isn't working.
> Here's an example inspired by the tutorial
> (http://avro.apache.org/docs/1.7.2/api/cpp/html/index.html). Using their
> cpx.json
> {noformat}
> 00001 {
> 00002 "type": "record",
> 00003 "name": "cpx",
> 00004 "fields" : [
> 00005 {"name": "re", "type": "double"},
> 00006 {"name": "im", "type" : "double"}
> 00007 ]
> 00008 }
> {noformat}
> Generating cpx.hh by
> avrogencpp -i cpx.json -o cpx.hh -n c
> The test program is then:
> {code:java}
> 1#include "cpx.hh"
> 2#include "avro/Compiler.hh"
> 3#include "avro/Encoder.hh"
> 4#include "avro/Decoder.hh"
> 5#include "avro/Specific.hh"
> 6#include "avro/Generic.hh"
> 7#include <sstream>
> 8#include <fstream>
> 9
> 10using namespace std;
> 11int main()
> 12{
> 13 ifstream ifs("cpx.json");
> 14 avro::ValidSchema type_schema;
> 15 avro::compileJsonSchema(ifs, type_schema);
> 16
> 17 ostringstream oss (ostringstream::out);
> 18 oss.precision(30); // doesn't matter
>
>
> 19 std::auto_ptr<avro::OutputStream> out = avro::ostreamOutputStream(oss);
> 20 avro::EncoderPtr e = avro::jsonEncoder(type_schema);
> 21 e->init(*out);
> 22 c::cpx complex;
> 23 complex.re = 1.123456789;
> 24 complex.im = 2.01;
> 25 avro::encode(*e, complex);
> 26 e->flush();
> 27 cout.precision(30);
> 28 cout << oss.str() << endl;
> 29
> 30 return 0;
> 31}
> {code}
> If we then compile and run this we get:
> {"re":1.12346,"im":2.01}
> Where as I'd expect something like:
> {"re":1.12346789,"im":2.01}
> It doesn't seem to matter where/if we set the precision on the output stream
> (line 18).
> Is there a different way to handle this? How do I keep the precision from
> getting stripped off double when doing json encoding?
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