C Preprocessor - Use definitions as integer and as wide strings

Question

The version number in my code is defined in a few formats which requires me to change more than one definition when I go up in the version:

#define VERSION_N       0x0203
#define SERIALNUMBER_STR    L"2.0.3"

and so on.

I'd like to centralize it to one single definition. Something like:

#define VER_X_  0
#define VER_H_  2
#define VER_M_  0
#define VER_L_  3

#define VERSION_N   VER_L_ + 0x10*VER_M_ + 0x100*VER_H_ + 0x1000*VER_X_
#define SERIALNUMBER_STR    ??????????????

You should put parentheses around your macro bodies to prevent surprises due to operator precedence at the expansion site. i.e. 2*VERSION_N will give you the wrong result because it will only multiply the VER_L_ by 2 since * has higher precedence than +. — pat
– pat, Commented Mar 2, 2014 at 22:27
@pat Interesting. Should be put in the final solution though irrelevant in my case. Tx. — Shaul
– Shaul, Commented Mar 3, 2014 at 8:22
Who started the obsession with trailing underscores in macro names? — Jens
– Jens, Commented May 14, 2016 at 9:23
@Shaul the currently accepted answer (written by you) is misleading and even after the edits back in 2014 it is still incorrect. The other answer by ouah is the best -- please consider accepting that answer instead, to assist future visitors to Stack Overflow. — paddy
– paddy, Commented Mar 26, 2021 at 1:45

ouah · Accepted Answer · 2014-03-04 18:21:58Z

3

Use a stringify macro:

#define STRINGIFY_1(x...)   #x
#define STRINGIFY(x...)     STRINGIFY_1(x)

#define VER_X_  0
#define VER_H_  2
#define VER_M_  0
#define VER_L_  3

#define SERIALNUMBER_STR  STRINGIFY(VER_H_) L"." STRINGIFY(VER_M_)  \
                          L"." STRINGIFY(VER_L_)

EDIT1: I added the L in L"." to have wide strings. I don't put a L#x as it got expanded with a space and something in the form L "string" is not a string literal in C. Nevertheless concatenating a string literal and a wide string literal result in a wide string literal.

EDIT2: As put in the comments, the example above work with the last revisions of C (c99 and c11) but not with c89 (i.e., not with MSVC). First reason is variadic macros are not supported in c89. The second reason is in c99 you can concatenate a character string literal and a wide string literal but in c89 this is undefined behavior. Below is a standard solution that also work in c89:

#define CAT(x, y)  x##y
#define WIDE(x)    CAT(L,x)

#define STRINGIFY_1(x)   #x
#define STRINGIFY(x)     STRINGIFY_1(x)

#define VER_X_  0
#define VER_H_  2
#define VER_M_  0
#define VER_L_  3

#define SERIALNUMBER_STR  WIDE(STRINGIFY(VER_H_)) L"." WIDE(STRINGIFY(VER_M_))  \
                          L"." WIDE(STRINGIFY(VER_L_))

edited Mar 4, 2014 at 18:21

answered Mar 2, 2014 at 21:40

ouah

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4 Comments

Shaul Over a year ago

Not compiling. Perhaps not supported by MS (I'm using Build 6.0) Also, I need a wide char string.

ouah Over a year ago

@Shaul MSVC does not support c99, remove the ... in the macro and it will work with MSVC.

Shaul Over a year ago

MS did not accept the change. Error message is: error C2308: concatenating mismatched strings.

ouah Over a year ago

@Shaul another c89 issue. Concatenating wide string literal and character string literal is OK in c99 (and the result is a wide string literal) but is undefined behavior in c89.

Shaul · Accepted Answer · 2014-03-03 08:30:09Z

0

Here's the tested solution:

#define VER_X_  0
#define VER_H_  2
#define VER_M_  0
#define VER_L_  3



#define VERSION_N (VER_L_ + 0x10*VER_M_ + 0x100*VER_H_ + 0x1000*VER_X_)

// Device Strings
//
#define STRINGIFY_1(x)   L#x
#define STRINGIFY(x)     STRINGIFY_1(x)
#define PASTE(x, y) x##y
#define MAKEWIDE(x) PASTE(L,x)

#define SERIALNUMBER_STR MAKEWIDE(STRINGIFY(VER_H_)) L"." \
                         MAKEWIDE(STRINGIFY(VER_M_)) L"." \
                         MAKEWIDE(STRINGIFY(VER_L_))

Thanks to ouah

EDIT:

Added parentheses according to pat.
Ouah's remark was taken seriously. Solution adapted to suit MS: Added two PASTE & MAKEWIDE

edited Mar 3, 2014 at 8:30

answered Mar 2, 2014 at 21:59

Shaul

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2 Comments

ouah Over a year ago

see the edit in my answer for wide strings, you should not use L#x.

Jens Over a year ago

Just my personal taste, but I find the original two macros better in any way. What you ended up with is a lot of obfuscation.

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