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[GH-ISSUE #63] Temporary files on Windows #52

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opened 2026-05-05 11:32:10 -06:00 by gitea-mirror · 7 comments

gitea-mirror commented

2026-05-05 11:32:10 -06:00

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Originally created by @utelle on GitHub (Jul 6, 2016).
Original GitHub issue: https://github.com/jmcnamara/libxlsxwriter/issues/63

Originally assigned to: @jmcnamara on GitHub.

This issue is somewhat related to issue #53, but that one has a misleading subject.

On Windows the current default implementation of lxw_tmpfile (which uses tmpfile under the hood) can impose a real problem. According to the documentation tmpfile always creates temporary files in the root directory. However, the root directory is not accessible for users without elevated rights. This makes libxlsxwriter fail and results in zero-length Excel files.

The alternative implementation might be ok on Linux systems, but doesn't work on Windows. And a hard-coded path isn't a good idea anyway.

In the meantime I implemented a Windows and MSVC specific solution and of course I can post it here.

Additionally you can find under the following link a generic implementation: An all-singing, all-dancing C function to create a temporary file. Maybe this could be a generic solution for creating temporary files.

Originally created by @utelle on GitHub (Jul 6, 2016). Original GitHub issue: https://github.com/jmcnamara/libxlsxwriter/issues/63 Originally assigned to: @jmcnamara on GitHub. This issue is somewhat related to issue #53, but that one has a misleading subject. On Windows the current default implementation of `lxw_tmpfile` (which uses `tmpfile` under the hood) can impose a real problem. According to the documentation `tmpfile` always creates temporary files in the root directory. However, the root directory is not accessible for users without elevated rights. This makes `libxlsxwriter` fail and results in zero-length Excel files. The alternative implementation might be ok on Linux systems, but doesn't work on Windows. And a hard-coded path isn't a good idea anyway. In the meantime I implemented a Windows and MSVC specific solution and of course I can post it here. Additionally you can find under the following link a generic implementation: [An all-singing, all-dancing C function to create a temporary file](http://www.di-mgt.com.au/c_function_to_create_temp_file.html). Maybe this could be a generic solution for creating temporary files.

gitea-mirror

2026-05-05 11:32:10 -06:00

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gitea-mirror commented

2026-05-05 11:32:20 -06:00

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@jmcnamara commented on GitHub (Jul 6, 2016):

Hi Ulrich,

According to the documentation tmpfile always creates temporary files in the root directory.

That incredible piece of software engineering has been a thorn in my side for years. The Perl and Python versions of this library have options to override the default temp directory.

In the meantime I implemented a Windows and MSVC specific solution and of course I can post it here.

Yes. That might help someone else who is struggling with this problem.

Maybe this could be a generic solution for creating temporary files.

I'm little reticent to include something like this but there may be no choice for Windows users. I'll look into adding it on a branch for testing and take it from there.

John

@jmcnamara commented on GitHub (Jul 6, 2016): Hi Ulrich, > According to the documentation tmpfile always creates temporary files in the root directory. That incredible piece of software engineering has been a thorn in my side for years. The Perl and Python versions of this library have options to override the default temp directory. > In the meantime I implemented a Windows and MSVC specific solution and of course I can post it here. Yes. That might help someone else who is struggling with this problem. > Maybe this could be a generic solution for creating temporary files. I'm little reticent to include something like this but there may be no choice for Windows users. I'll look into adding it on a branch for testing and take it from there. John

gitea-mirror commented

2026-05-05 11:32:24 -06:00

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@utelle commented on GitHub (Jul 8, 2016):

Hi John,

sorry for the delay. I was busy in my job.

In the meantime I implemented a Windows and MSVC specific solution and of course I can post it here.

Yes. That might help someone else who is struggling with this problem.

I'll try to provide a variant that might be usable not only with MSVC. Not sure whether I succeed. I'll post the code early next week.

In fact, my implementation is similar to the generic implementation I quoted - just without the unneeded bits and pieces.

@utelle commented on GitHub (Jul 8, 2016): Hi John, sorry for the delay. I was busy in my job. > > In the meantime I implemented a Windows and MSVC specific solution and of course I can post it here. > > Yes. That might help someone else who is struggling with this problem. I'll try to provide a variant that might be usable not only with MSVC. Not sure whether I succeed. I'll post the code early next week. In fact, my implementation is similar to the generic implementation I quoted - just without the unneeded bits and pieces.

gitea-mirror commented

2026-05-05 11:32:27 -06:00

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@jmcnamara commented on GitHub (Jul 8, 2016):

sorry for the delay. I was busy in my job.

No problem. We all have jobs and probably none of them relate to creating Excel files for a living.

I'll try to provide a variant that might be usable not only with MSVC. Not sure whether I succeed. I'll post the code early next week.

In fact, my implementation is similar to the generic implementation I quoted - just without the unneeded bits and pieces.

I'm going to put together a branch with the above library as an optional make option on Unix and as the default on Windows. I'll ping you when I've implemented and tested it a bit. If it looks stable I'll merge it to master.

@jmcnamara commented on GitHub (Jul 8, 2016): > sorry for the delay. I was busy in my job. No problem. We all have jobs and probably none of them relate to creating Excel files for a living. > I'll try to provide a variant that might be usable not only with MSVC. Not sure whether I succeed. I'll post the code early next week. > > In fact, my implementation is similar to the generic implementation I quoted - just without the unneeded bits and pieces. I'm going to put together a branch with the above library as an optional make option on Unix and as the default on Windows. I'll ping you when I've implemented and tested it a bit. If it looks stable I'll merge it to master.

gitea-mirror commented

2026-05-05 11:32:30 -06:00

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@jmcnamara commented on GitHub (Jul 10, 2016):

I've pushed a version using tmpfileplus as the default tmpfile handler to the following branch: https://github.com/jmcnamara/libxlsxwriter/tree/tmpfileplus

I need to add some more documentation and fix the Mac cocoapod files but if you get a chance you can test it to see if it works for you.

@jmcnamara commented on GitHub (Jul 10, 2016): I've pushed a version using tmpfileplus as the default tmpfile handler to the following branch: https://github.com/jmcnamara/libxlsxwriter/tree/tmpfileplus I need to add some more documentation and fix the Mac cocoapod files but if you get a chance you can test it to see if it works for you.

gitea-mirror commented

2026-05-05 11:32:33 -06:00

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@utelle commented on GitHub (Jul 11, 2016):

I will test it within the next few days.

I inspected the code of tmpfileplus. The approach seems to be more or less the same as what I had implemented in my local version. That is, I think I can forego to publish my own implementation.

@utelle commented on GitHub (Jul 11, 2016): I will test it within the next few days. I inspected the code of `tmpfileplus`. The approach seems to be more or less the same as what I had implemented in my local version. That is, I think I can forego to publish my own implementation.

gitea-mirror commented

2026-05-05 11:32:36 -06:00

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@utelle commented on GitHub (Jul 11, 2016):

I tested the new implementation. It works as expected.

There is only one thing that I don't like in tmpfileplus: as default it uses the filename prefix tmp. making the random part of the filename in fact the filename extension. In case the temporary files are not deleted automatically for some reason or need to be inspected during debugging, this makes it difficult to locate the files. I would prefer a default prefix tmp_ or tmp- or libxlsxwriter or no prefix at all. This can easily be achieved by calling tmpfileplus in function lxw_tmpfile with a not-NULL prefix parameter like

    return tmpfileplus(tmpdir, "libxlsxwriter", NULL, 0);

Alternatively, the default value in tmpfileplus could be changed.

@utelle commented on GitHub (Jul 11, 2016): I tested the new implementation. It works as expected. There is only one thing that I don't like in `tmpfileplus`: as default it uses the filename prefix `tmp.` making the random part of the filename in fact the filename extension. In case the temporary files are not deleted automatically for some reason or need to be inspected during debugging, this makes it difficult to locate the files. I would prefer a default prefix `tmp_` or `tmp-` or `libxlsxwriter` or no prefix at all. This can easily be achieved by calling `tmpfileplus` in function `lxw_tmpfile` with a not-NULL prefix parameter like ``` return tmpfileplus(tmpdir, "libxlsxwriter", NULL, 0); ``` Alternatively, the default value in `tmpfileplus` could be changed.

gitea-mirror commented

2026-05-05 11:32:39 -06:00

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@jmcnamara commented on GitHub (Jul 11, 2016):

I've left the prefix as it is. If it becomes a real issue for someone I'll change it.

I've merged the tmpfile changes down to master and pushed them in the 0.4.1 release: http://libxlsxwriter.github.io/changes.html

Thanks for the report. Closing.

@jmcnamara commented on GitHub (Jul 11, 2016): I've left the prefix as it is. If it becomes a real issue for someone I'll change it. I've merged the tmpfile changes down to master and pushed them in the 0.4.1 release: http://libxlsxwriter.github.io/changes.html Thanks for the report. Closing.