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[GH-ISSUE #413] Unit tests won't run when using Microsoft C compiler #327

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opened 2026-05-05 12:09:19 -06:00 by gitea-mirror · 6 comments

gitea-mirror commented

2026-05-05 12:09:19 -06:00

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Originally created by @HolgiHo on GitHub (Sep 18, 2023).
Original GitHub issue: https://github.com/jmcnamara/libxlsxwriter/issues/413

When using the Microsoft C compiler (Visual Studio / VS Build Tools), the unit test registration in ctest.h does not work (and has apparently never worked before). The unit test executable xlsxwriter_unit.exe simply executes zero test cases.

Reason: The test case registration macro CTEST(...) works by adding instances of struct ctest to a special linker segments (on *nix platforms). When using MSC, the structs are added to the normal data segment and thus cannot be found by the test case driver in ctest_main.

Solution: Use linker segments also in MSC. This requires a special syntax, as linker segments specifications are not portable between platforms.

PR will follow shortly.

Originally created by @HolgiHo on GitHub (Sep 18, 2023). Original GitHub issue: https://github.com/jmcnamara/libxlsxwriter/issues/413 When using the Microsoft C compiler (Visual Studio / VS Build Tools), the unit test registration in `ctest.h` does not work (and has apparently never worked before). The unit test executable `xlsxwriter_unit.exe` simply executes zero test cases. Reason: The test case registration macro `CTEST(...)` works by adding instances of `struct ctest` to a special linker segments (on *nix platforms). When using MSC, the structs are added to the normal data segment and thus cannot be found by the test case driver in `ctest_main`. Solution: Use linker segments also in MSC. This requires a special syntax, as linker segments specifications are not portable between platforms. PR will follow shortly.

gitea-mirror closed this issue

2026-05-05 12:09:21 -06:00

gitea-mirror commented

2026-05-05 12:09:24 -06:00

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@jmcnamara commented on GitHub (Sep 18, 2023):

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: https://github.com/bvdberg/ctest/pull/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?

@jmcnamara commented on GitHub (Sep 18, 2023): 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: https://github.com/bvdberg/ctest/pull/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?

gitea-mirror commented

2026-05-05 12:09:25 -06:00

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@HolgiHo commented on GitHub (Sep 19, 2023):

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.

@HolgiHo commented on GitHub (Sep 19, 2023): ### 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.

gitea-mirror commented

2026-05-05 12:09:26 -06:00

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@jmcnamara commented on GitHub (Sep 23, 2023):

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 commented on GitHub (Sep 23, 2023): > 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](https://github.com/jmcnamara/libxlsxwriter/blob/main/test/cpp/test_compilation.cpp) 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.

gitea-mirror commented

2026-05-05 12:09:27 -06:00

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@jmcnamara commented on GitHub (Sep 25, 2023):

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 commented on GitHub (Sep 25, 2023): 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.

gitea-mirror commented

2026-05-05 12:09:28 -06:00

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@jmcnamara commented on GitHub (Sep 25, 2023):

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 commented on GitHub (Sep 25, 2023): 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.

gitea-mirror commented

2026-05-05 12:09:29 -06:00

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@jmcnamara commented on GitHub (Sep 26, 2023):

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.

@jmcnamara commented on GitHub (Sep 26, 2023): 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.