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How to check a value like "#define VERSION 3.1.4" at compile time?

I am adding compile-time checks to my C ++ projects to make sure that third-party libraries on all development machines and build servers are updated. Most libraries define something like the following, for example. version 3.1.4:

#define VERSION_MAJOR 3 #define VERSION_MINOR 1 #define VERSION_BUILD 4

This is convenient and easy to verify using the static_assert directives or preprocessor.

Now I look at a third-party library that defines only one macro:

 #define VERSION 3.1.4

How can I check the value of such a macro at compile time?

With C ++ 11, I could use the constexpr string comparison function and constexpr macro to test it:

 constexpr bool static_equal(const char * a, const char * b) { return (*a == *b) && (*a == '\0' || static_equal(a + 1, b + 1)); } // stringification functions #define str(x) #x #define xstr(x) str(x) static_assert(static_equal(xstr(VERSION), "3.1.4"), "incorrect version of libwhatever");

But we use Visual Studio 2013 on Windows machines, so I can only use the subset of C ++ 11 that it supports. Unfortunately, constexpr not supported.

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c ++ c-preprocessor c ++ 11
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Here is what I am doing now:

 #define str(x) #x #define xstr(x) str(x) #include xstr(libwhatever.version.is.VERSION.should.be.3.1.4)

Along with this, I add an empty file to the project called libwhatever.version.is.3.1.4.should.be.3.1.4 . Therefore, if the version is correct, the preprocessor will successfully include this file. Otherwise, it will not work with “Can not open” libwhatever.version.is.2.7.2.should.be.3.1.4 ', there is no such file or directory. "And the failure of the assembly with a somewhat meaningful message is that considered at the end.

Of course, this approach is not very flexible; for example, I cannot check the minimum version or a number of versions. But for me it is enough to check the exact value.

This is similar to working with Visual C ++ as well as with g ++. I am not sure that the behavior is fully defined according to the standard.

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You cannot in the preprocessor, but you can abuse character traits!

VS 2013 seems to support variation patterns. Try using the CSTRING macro at fooobar.com/questions/52916 / ... (you can replace constexpr with const and have the code still working) and do something like:

 #define STRT(x) decltype(CSTRING(x)) static_assert(std::is_same<STRT(VERSION), STRT("3.1.4")>::value, "incorrect version of libwhatever");

EDIT: This does not work. However, if your compiler compiles this without errors:

 extern const char data[] = "abc"; template <char C> struct x { static const char c = C; }; char buf[(int)x<"ABC123"[0]>::c]; int main() { return (int)buf; }

Then you can try the following:

 #include <type_traits> #define VERSION 1.2.3 #define STR2(x) #x #define STR(x) STR2(x) template <char...> struct ststring; // https://stackoverflow.com/a/15860416/2097780 #define MACRO_GET_1(str, i) \ (sizeof(str) > (i) ? str[(i)] : 0) #define MACRO_GET_4(str, i) \ MACRO_GET_1(str, i+0), \ MACRO_GET_1(str, i+1), \ MACRO_GET_1(str, i+2), \ MACRO_GET_1(str, i+3) #define MACRO_GET_16(str, i) \ MACRO_GET_4(str, i+0), \ MACRO_GET_4(str, i+4), \ MACRO_GET_4(str, i+8), \ MACRO_GET_4(str, i+12) #define MACRO_GET_64(str, i) \ MACRO_GET_16(str, i+0), \ MACRO_GET_16(str, i+16), \ MACRO_GET_16(str, i+32), \ MACRO_GET_16(str, i+48) #define MACRO_GET_STR(str) MACRO_GET_64(str, 0), 0 static_assert(std::is_same<ststring<MACRO_GET_STR(STR(VERSION))>, ststring<MACRO_GET_STR("1.2.3")>>::value, "invalid library version");
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If you right-click on your project-> Properties-> Build Events-> Pre-Build, you will see the "Command Prompt" option. You can put the call into another program here.

You can write another C ++ program or any other language that you prefer that checks your file (or any number of files you want) for "#define VERSION 3.1.4". You can interrupt your build and put any warnings you want into this program.

here is the tutorial: https://dillieodigital.wordpress.com/2012/11/27/quick-tip-aborting-builds-in-visual-studio-based-on-file-contents/

: https://msdn.microsoft.com/en-us/library/e85wte0k.aspx

I tried to mess around with preprocessor commands for a long time, and I could not find a way to do this using only preprocessor commands.

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