About the use of connectors in C language # # # macro Stringize

First, demand-oriented, small projects, code is not many, version is quite a lot ...

You plan to use a macro to control the switch options, and then pass a long string

#if

#elif

...

#endif

To control the build version number, but also according to compatibility and minor changes to do the level three version number ....

So we need a version number splicing, obviously, it should be the compile time can be done.

--------Demand is complete--------

The C-language macro definition should be complete and even more problematic during code execution.

Although string.h can also be used to complete stitching.

Uncomfortable, Skinner.

Preliminary find using # and # #, can be completed, further find out what a #@ is ... Some compilers do not support

After a preliminary trial # will directly transfer the macro directly into the string,#@ in theory is to achieve the function I need, but does not support

---------------Magical Split-line-------------------------

further search stringize site:gcc.gnu.org

Find page

3.4 stringification

Https://gcc.gnu.org/onlinedocs/cpp/Stringification.html

In view of the blog, it is not affixed to the original, but also need to see their own.

Conclusion:

If you want to stringify the result of expansion of a macro argument, you had to use both levels of macros.

#define XSTR (s) str (s)     #define STR (s) #s     #define FOO 4     str (foo)          ==> "foo"     xstr (foo)          ==> XSTR (4)          ==> str (4)          ==> "4"

The combination # # infinite possibility comes out

#define XSTR (s) str (s)      //copy from Https://gcc.gnu.org/onlinedocs/cpp/Stringification.html#define str (s) #s # Define _STRING_ (_x_)           xstr (_x_)    //convert from macro to STRING #define Bsp_hard_reversion 1.0.0#define      sw_ First_version        8#define sw_mid_version          800#define sw_last_version         021#define sw_full_vsersion        SW_ first_version##.# #SW_MID_VERSION ##.# #SW_LAST_VERSION # define hw_version_string       _string_ (bsp_hard_reversion) # Define sw_version_string       _string_ (sw_full_vsersion) static const char hw_rev[] = hw_version_string;      Hw_rec Config by boards.hstatic const char fw_rev[] = "8.0.0"; static const char sw_rev[] = sw_version_string; #undef str# undef xstr#undef _string_

OK to here I need the function has been done. Everybody just take a debugging tool to see it, it's OK.

Careful study of the implementation of the principle, feel their own understanding of the definition of the macro into a level ... It's not that complicated, actually.

S was stringified when it was used in Str, so it was not macro-expanded first. But s are an ordinary argument to Xstr, so it's completely macro-expanded before Xstr itself is Expanded ( see Argument prescan). Therefore, by the time str gets to its argument, it has already been macro-expanded.

Original address

http://my.oschina.net/mummy108/blog/510439

About the use of connectors in C language # # # macro Stringize