C macro to transform a SVN revision to an integer

Question

I am looking for a C/C++ macro that can transform a random SVN revision like "$Revision: 9 $" or "$Revision: 9999999 $" into an integer or a string.

I know that simple functions exists to achieve this, but I want this to be made at compile time.

My wish is to write things like:unsigned int rev = SVN_TO_INT("$Revision$");

Answer 1

I'm relatively sure that this isn't possible with a macro.

It may be possible with template metaprogramming, but I've never gone near it.

It would also be possible with a pre-build script that replaces SVN_TO_INT with your desired text.

I don't understand why you want this, though, since it would be just as easy to hardcode the version number since you know it at compile time.

Answer 2

You can't fully work with strings at preprocessing or compile time - but why not use something something like:

int svn_version() 
{
     static const int v = extract_svn_version(REVISION);
     return v;
}

Answer 3

You can't do the kind of string manipulation you want at compile time with the C preprocessor (macros) or with templates (C++). You'll need to use an external utility or script that you can invoke from the build process.

Some utilities/scripts/code that might help you:

• SvnRev: http://www.compuphase.com/svnrev.htm
• http://blog.guymahieu.com/2008/06/09/getting-the-svn-head-revision-number-from-a-windows-batch-file/
• http://www.codeproject.com/KB/architecture/svn%5Fvisual%5Fstudio.aspx

Answer 4

I agree that you can't work with strings at compile time through macros or templates. So.... don't use strings.

This is an ugly hack, but I think it meets all your requirements. I don't recommend it.

#define $Revision struct REV_STR { unsigned foo
#define $ * 64; };

$Revision: 4521 $

enum { REV = sizeof(REV_STR) / 8 };

#undef $Revision
#undef $

#include <iostream>
int main()
{
   std::cout << REV << std::endl;
   return 0;
}

// $ g++ -Wall -Wextra revision.cpp && ./a.exe
// revision.cpp:4: warning: width of `REV_STR::foo' exceeds its type
// 4521

Answer 5

I agree that it is not doable with macros, however, I found a trick using compiler optimizations. The result is that the expression JL_SvnRevToInt("$Revision: 12345 $") is reduced to a single unsigned integer: 12345

inline unsigned int JL_SvnRevToInt(const char *r) {


    if ( r == NULL || r[0] == '\0' || r[10] == '\0' || r[11] == '\0' || r[12] == '\0' || r[13] == '\0' )
    return 0;

    const unsigned int count = 
       r[11] == ' ' ? 1
     : r[12] == ' ' ? 10
     : r[13] == ' ' ? 100
     : r[14] == ' ' ? 1000
     : r[15] == ' ' ? 10000
     : r[16] == ' ' ? 100000
     : r[17] == ' ' ? 1000000
     : r[18] == ' ' ? 10000000
     : r[19] == ' ' ? 100000000
     : 0;

    return
     (r[11] == ' ' ? 0 : (r[11]-'0') * (count/10) +
     (r[12] == ' ' ? 0 : (r[12]-'0') * (count/100) + 
     (r[13] == ' ' ? 0 : (r[13]-'0') * (count/1000) + 
     (r[14] == ' ' ? 0 : (r[14]-'0') * (count/10000) + 
     (r[15] == ' ' ? 0 : (r[15]-'0') * (count/100000) +
     (r[16] == ' ' ? 0 : (r[16]-'0') * (count/1000000) +
     (r[17] == ' ' ? 0 : (r[17]-'0') * (count/10000000) +
     (r[18] == ' ' ? 0 : (r[18]-'0') * (count/100000000) +
     (r[19] == ' ' ? 0 : (r[19]-'0') * (count/1000000000) +
     0)))))))));
}

It supports9 digits revision number, NULL and empty and "$Revision$" strings.

Answer 6

If you have a makefile based build system you can make a special rule that creates a file every make time.

.PHONY: svn_revision.c

svn_revision.c:
        echo -n "int svn_revision = " > svn_revision.c
        svn info | grep Revision | cut -f2 -d" " >> svn_revision.c
        echo ";"  >> svn_revision.c

svn_revision.o: svn_revision.c