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  1. JDK
  2. JDK-4616318

Spec for JNI's GetStringChars() is incomplete

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: P4
    • Resolution: Won't Fix
    • Affects Version/s: 1.3.0
    • Fix Version/s: None
    • Component/s: docs
    • Labels:
    • Subcomponent:
    • CPU:
      x86
    • OS:
      linux

      Description

      Name: jl125535 Date: 12/19/2001


      FULL PRODUCT VERSION :
      java version "1.3.1_01"
      Java(TM) Runtime Environment, Standard Edition (build
      1.3.1_01)
      Java Hotspot(TM) Client VM (build 1.3.1_01, mixed mode)


      Not applicable.



      A DESCRIPTION OF THE PROBLEM :
      I recently unwittingly stumbled across an undocumented
      feature of the JNI method "GetStringChars()" which has
      wasted quite a bit of my time. I discovered that sometimes
      the strings I was getting returned from GetStringChars() on
      the native side were not the length I expected.

      After a quick search on bug parade, I found bug #4076576,
      which mentions the fact that "Java strings are not
      NULL-terminated. Thus the string returned by GetStringChars
      does not have 0 at the end."

      I am not reporting this as a bug in itself. There are
      probably good reasons why the JNI was designed to not return
      null-terminated strings. What I *am* reporting as a bug, is
      that the fact that the strings are *not* necessarily
      null-terminated is not documented anywhere in the JNI
      documentation (including the latest JDK 1.4 documentation on
      your website). In fact, the only place I have ever seen this
      documented is in bug report #4076576. This is highly
      unsatisfactory, for a number of reasons:

      1. C programmers, in the absence of any documentation to the
      contrary, will generally assume that the strings they are
      passed are NULL-terminated.
      2. In the case where the programmer is unsure and decides to
      investigate for themselves, they may find that (by
      coincidence) the strings that they get happen to be
      NULL-terminated, and incorrectly assume that this will
      always be the case (which is what I did). This may introduce
      bugs at a later stage.
      3. The JNI tutorial ("Accessing Java Strings in Native
      Methods") mentions that the strings returned by
      GetStringUTFChars() is NULL-terminated. This would lead many
      developers to conclude that GetStringChars() would also be
      NULL-terminated (again, this is what I did).

      The complaints about lack of documentation were actually
      already made in the comments of bug report #4076576. However
      nothing seems to have been done about it in the 4 years
      since the original report was made and that bug has long
      since been closed. Thus I thought the particular complaint
      about lack of documentation was worth submitting as a bug in
      itself - especially as it is still causing developers (such
      as myself) to be caught out.


      STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
      1. Read the documentation.
      2. See that it is incomplete.

      This bug can be reproduced always.

      ---------- BEGIN SOURCE ----------
      See bug #4076576
      ---------- END SOURCE ----------

      CUSTOMER WORKAROUND :
      Once the behaviour of GetStringChars() is properly
      understood, work-around is easy - if a null-terminated
      string is required, then make a copy and null-terminate it
      yourself.
      (Review ID: 137530)
      ======================================================================

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              Assignee:
              santhoshla Santhosh La (Inactive)
              Reporter:
              jleesunw Jon Lee (Inactive)
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