How to implement mbtowc for android? (or, ideally, how not to?)

Issue

I am attempting to build an Android app that makes use of boost serialization. I have built the library against NDK r8d using arm 4.7's g++. When I go to compile my native code into a library using ndk-build, however, I get "undefined reference to 'mbtowc'" and "undefined reference to 'wctomb'" when the compiler attempts to link some code from Archive headers in boost.

I cannot seem to get a clear answer as to whether the NDK supports these functions.

Although it implements the functions, the CrystaX NDK is not an option as it has known crashes when using it with Boost, according to the Boost mailing list.

So, if the NDK does implement these functions somehow, why is NDK-build unable to link against them? I can find reference to them in cstdlib within the NDK, and I believe there may be a flag I need to set, but I'm not sure how or where to do so.

If there is no implementation of them, does anyone have any advice on how I can write them myself? I know roughly what mbtowc and its complement are supposed to do, but without much experience writing low-level C, and without much knowledge of Android / ARM architecture, I could really use some advice on doing so.

Solution

Findings! Yes, boost has options to build it without requiring wchar support by adding preprocessor definitions to the boost build scripts. Boost still crashes when built using them at the line of code where I attempt to serialize an object to file. (the crash is a generic segfault at 0x00000000, and I was unable to gain any useful information).

So, I haven't bothered writing wctomb or its inverse. I shouldn't need to, is the answer to my question, although in the end the answer to the question doesn't matter.

To further clarify: don't bother doing what I've been trying to do. If you have been using Boost's serialization library and want your code to run on android ndk r8d or earlier, just give up. Write a serializer yourself, because there is no useful information to be found on how to make Serialization work. Hopefully a future release of the ndk fixes this problem, but for now I have no choice but to just rewrite everything.

Answered By - Wes Paugh