Unit tests won't run when using Microsoft C compiler about libxlsxwriter

[jmcnamara]

Thanks for the report.

Solution: Use linker segments also in MSC.

There is an upstream PR to fix this in ctest but it doesn't seem to have been merged: bvdberg/ctest#35

I'd prefer not to include local fixes for this issue so I think I will pass on this.

The PR also includes some other fixes: "fix build error in VS: use const char* in struct lxw_header_footer_options". Any idea why this doesn't show up in the "CMake on Windows" CI test?

[HolgiHo]

VS build error

The error occurs when compiling the following code in a C++ file, even when xlsxwriter.h uses the extern "C" { ... } declaration.

lxw_header_footer_options header_options;
header_options.image_left = "logo_small.png";

gives error C2440: '=': cannot convert from 'const char [15]' to 'char *'
This works in C, so cmake builds don't complain. However, it should be possible to use the struct members also from a C++ implementation file without writing strange things like

header_options.image_left = const_cast<char*>("logo_small.png");

using const char* for image_strings[] in _worksheet_set_header_footer_image is not really required as this is always C code, but it's cleaner.

ctest

I saw ctest.h was already modified (see its git log) to "work" on Windows. So I wondered that it compiles, but no tests are found.

IMHO, in the short term, working unit tests under Windows are important for libxlsxwriter development. The ctest repository seems to be a bit abandoned, so I doubt if the PR you mentioned will ever be merged into ctest, also because there are lots of guesses and no clear statements how the MS compiler works. (The source of truth is here I think: https://devblogs.microsoft.com/oldnewthing/20181107-00/?p=100155 and the two follow-up articles.)

I mean, if ctest once supports MSVC, you can simply copy the latest version from there and you're done.

[jmcnamara]

The error occurs when compiling the following code in a C++ file, even when xlsxwriter.h uses the extern "C" { ... } declaration.

Thanks for flagging this. I'll look into that separately. I have a simple test to ensure CPP compatible const char* in the APIs but it doesn't flag them in structs or assignments so I'm going to work on that for a bit to see if I can have better automated tests.

After that I'll look at the unit test part of the PR. I just need to figure out if I should upgrade to the latest ctest.h before adding this fix.

[jmcnamara]

I've added a fix to change all the public "char*" members to "const char*". You can try it when you get a chance.

I'll look into the ctest.h issue next. It is likely that I will upgrade to the latest version. The previous version I used with from 2014 with local fixes over time.

[jmcnamara]

I updated ctest.h to the latest version on the ctest branch. It works well for Unix-like systems but fails completely on Windows.

I think that rather than fix it I'd prefer to disable the unit test compilation on Windows. As you pointed out the tests didn't work previously so it probably isn't a big loss. The functional tests are more comprehensive anyway.

[jmcnamara]

In the end I went with the option of turning off the unit tests for MSVC until ctest.h supports it. I am going to close this and the PR. Thanks for the input.