Library built with 7.xx causes warning message in 8.xx or later

Introduction　

Because both the size and the internal encoding of wchar_t are different between IAR Embedded Workbench for Arm version 7.xx and version 8.xx or later, the linker message

Warning [Lt009]: Inconsistent wchar_t size

will be generated when a library built with version 7.xx is used in version 8.xx or later.

Discussion

In IAR Embedded Workbench for Arm version 7.80 and earlier, the size of wchar_t was two bytes and in version 8.11 the size of wchar_t is four bytes. Moreover the internal encoding of wchar_t objects between these versions objects is different.

This means that combining object files built with versions 7.80 and 8.xx or later will generate a linker warning if the application uses wchar_t, the behavior will be unpredictable.

In general, we strongly recommend using object code from one version only, and for a major upgrade such as 7.xx to 8.xx or later, all code should be rebuilt.

If you choose to not to rebuilt, you should at least do following actions:

1. a)    Rebuild object code built with version 7.xx and written in C++.
2. b)    If the library does include wchar_t, rebuild the library with version 8.11 or later.
3. c)    If a library built with version 7.xx does not include wchar_t, and an application built with version 8.xx (or later) in fact works as expected, you might want to ignore the warning message.
   To suppress the warning message, do this:
   1. Choose Project>Options>Linker>Diagnostics
   2. Select Suppress these diagnostics  and specify: Lt009
   3. Click OK.

Note:
If you later add another 7.xx library to your 8.11 (or later) project, please remove the suppress diagnostic option described above (“Lt009”) and go through steps a-c again.

Conclusion

A library that uses wchar_t built with IAR Embedded Workbench for Arm version 7.xx must be rebuilt to be used with version 8.xx or later.

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