How to redefine (override) C++ DATE and TIME predefined macros in Visual Studio?

Question

Is there any possibility to redefine __DATE__ and __TIME__ predefined C++ macros (give them other than default values) in Microsoft Visual Studio?

I tried compiler option /D "__DATE__=\"Feb 10 2021\"" but I'm getting:

pch.cpp : warning C4117: macro name '__DATE__' is reserved, '#define' ignored

and no effect. Any idea except modification of the code (or a confirmation 'it is not possible')?

Reason: C++ project, that I have, has its builds versioned by date macro values (every build gets its version from __DATE__/__TIME__ values). I need to simulate an "older" build - basically, to cheat this versioning system. I don't need to change the macro value format. I also know about an option to have another user-defined macro mentioned by @Jabberwocky.

You can use #undef __DATE__ and #undef __TIME__ to undefine a macro so you can give it a different value. — Locke
– Locke, Commented Feb 15, 2021 at 13:19
All symbols with two leading underscores are reserved for the implementation. Creating a symbol like that is UB. source: timsong-cpp.github.io/cppwp/lex.name#3 — NathanOliver
– NathanOliver, Commented Feb 15, 2021 at 13:19
This is classic example of XY problem. Why do you need to do it? What is your actual goal? — Marek R
– Marek R, Commented Feb 15, 2021 at 13:22
If this problem is single event issue, then just change your system time for period of building. Best solution would be apply Jabberwockys answear. — Marek R
– Marek R, Commented Feb 15, 2021 at 13:59
You can try to use /u to undefine Microsoft-specific symbols that the compiler defines, see learn.microsoft.com/en-us/cpp/build/reference/… (I'm not sure if it works with standard macros like __DATE__ or only with additions made by MSVC). — icebp
– icebp, Commented Feb 15, 2021 at 13:59

Jabberwocky · Accepted Answer · 2021-02-15 13:54:29Z

2

No you can't. But you don't need to either. Don't use __DATE__ but e.g. BUILD_DATE and add this:

#ifndef BUILD_DATE
#define BUILD_DATE __DATE__
#endif

And compile with:

/D "BUILD_DATE=\"Feb 10 2021\""

Then you get the exact behaviour you want.

But if you really can't replace __DATE__ with something of your own as suggested, you're out of luck.

edited Feb 15, 2021 at 13:54

answered Feb 15, 2021 at 13:23

Jabberwocky

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2 Comments

Lundin Over a year ago

Probably they wanted a useful date format like for example in the form of integers, instead of C's useless __DATE__ with months written as text.

Jabberwocky Over a year ago

@Lundin not sure because they wrote /D "__DATE__=\"Feb 10 2021\"" which is th exact useless format of __DATE__.

phuclv · Accepted Answer · 2024-12-10 01:50:34Z

One way is to fake the time that's perceived by MSVC cl.exe. This can be done by running the compiler inside a virtual machine (like Windows Sandbox) with a different time, or use some 3^rd party solution like RunAsDate to change the time of a process:

But probably what you want is reproducible builds. It's very important nowadays so lots of projects are moving toward it including Windows. There are /experimental:deterministic, /d1nodatetime and /Brepro flags in MSVC for this

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