C Preprocessor: Stringify int with leading zeros? - c
I've seen this topic which describes the "stringify" operation by doing:
#define STR_HELPER(x) #x
#define STR(x) STR_HELPER(x)
#define MAJOR_VER 2
#define MINOR_VER 6
#define MY_FILE "/home/user/.myapp" STR(MAJOR_VER) STR(MINOR_VER)
Is it possible to stringify with leading zeros? Let's say my MAJOR_REV needs to be two characters "02" in this case and MINOR_REV 4 characters "0006"
If I do:
#define MAJOR_VER 02
#define MINOR_VER 0006
The values will be treated as octal elsewhere in the application, which I don't want.
No clean nor handy way to do it. Just as a challenge, here a possible "solution":
1) create a header file (e.g. "smartver.h") containing:
#undef SMARTVER_HELPER_
#undef RESVER
#if VER < 10
#define SMARTVER_HELPER_(x) 000 ## x
#elif VER < 100
#define SMARTVER_HELPER_(x) 00 ## x
#elif VER < 1000
#define SMARTVER_HELPER_(x) 0 ## x
#else
#define SMARTVER_HELPER_(x) x
#endif
#define RESVER(x) SMARTVER_HELPER_(x)
2) In your source code, wherever you need a version number with leading zeroes:
#undef VER
#define VER ...your version number...
#include "smartver.h"
at this point, the expression RESVER(VER) is expanded as a four-digit sequence of character, and the expression STR(RESVER(VER)) is the equivalent string (NOTE: I have used the STR macro you posted in you answer).
The previous code matches the case of minor version in your example,it's trivial to modify it to match the "major version" case. But in truth I would use a simple external tool to produce the required strings.
I believe in the example provided by the question sprintf is the correct answer.
That said, there are a few instances where you really want to do this and with C preprocessor if there is a will and somebody stupid enough to write the code there is typically a way.
I wrote the macro FORMAT_3_ZERO(a) which creates a three digit zero padded number using brute force. It is in the file preprocessor_format_zero.h found at https://gist.github.com/lod/cd4c710053e0aeb67281158bfe85aeef as it is too large and ugly to inline.
Example usage
#include "preprocessor_format_zero.h"
#define CONCAT_(a,b) a#b
#define CONCAT(a,b) CONCAT_(a,b)
#define CUSTOM_PACK(a) cp_ ## a __attribute__( \
(section(CONCAT(".cpack.", FORMAT_3_ZERO(a))), \
aligned(1), used))
const int CUSTOM_PACK(23);
Related
Can C-preprocessor can output as a string the evaluation of compiled known constants values(e.g. 150000UL/1000UL)? #define arithmetics
I'm wondering if it can be written that the prepocessor evaluates assigned constants known at compile time and returns the result as a string. I believe the answer is no or complex, but I'll give a try. Basically I have constants which are expressed in milliseconds but I want to display the results as secs, therefore divide by 1000, and wonder because all is known at compile time, if the preprocessor can directly put the result of this division into the code rather than eval at runtime. Example: #define FREQ_AUTO_WHEN_RELAY_ON 150000UL #define STR_HELPER(x) #x #define STR(x) STR_HELPER(x) STR( FREQ_AUTO_WHEN_RELAY_ON/1000UL ) " secs" would yield to "150000UL/1000UL secs" which is not I want to display, aka "150 secs" Thanks
You have to first prepare a header with all possible outputs: // calculate.h #if VALUE == 1 #define RESULT 1 #elif VALUE == 2 #define RESULT 2 /* etc. millions of lines */ #elif VALUE == 150 #define RESULT 150 #endif Then you can do: #define VALUE FREQ_AUTO_WHEN_RELAY_ON/1000UL #include "calculate.h" STR(VALUE) Similarly, you first have to define a matrix of all possible combinations of values: #define DIV_1UL_1UL 1 #define DIV_1UL_2UL 0 #define DIV_2UL_1UL 2 /* etc. really millions of lines */ #define DIV_150000UL_1000UL 150 Then you can: #define DIV(a, b) DIV_##a##_##b #define XDIV(a, b) DIV(a, b) STR(XDIV(FREQ_AUTO_WHEN_RELAY_ON, 1000UL)) Can C-preprocessor can output as a string the evaluation of compiled known constants values(e.g. 150000UL/1000UL)? Yes, but it's not practical. Instead, generate the header file from a build system.
How do I concatenate two string macros in C?
I am trying to implement VERSION macro for my program, that is to be changed under certain circumstances. macro VERSION is defined via Makefile (git info is put there) and is a string. Now I have a set of #define'd switches and I want VERSION to reflect which of them are on. This looks now like the follows (main.h): #define COMPLEX_DEPOSITION // This is switch. later in code it is used in #ifdef...#endif construction. #ifdef COMPLEX_DEPOSITION #define CD "_COMP_DEP" // this is the string I want to put in the end of VERSION #define VERSION_ VERSION CD #undef VERSION // this is to suppress 'macro redefinition' warning #define VERSION VERSION_ #undef VERSION_ #endif Well, I get a lot of errors, most of which make me think that C preprocessor works with lines in file in random order:( Later I have an even more complex thing that is intended to make VERSION -> VERSION_WLT_GAP_2 #define WIRESLIFETIMES #ifdef WIRESLIFETIMES #define GAP 2 #define VERSION_ (VERSION ## "_WLT_GAP_" ## #GAP) #define VERSION VERSION_ #undef VERSION_ #endif and I got no idea what to do and if this is even possible
String literals concatenate naturally when placed next to each other "foo" "bar" is the same as "foobar". As for the second example, you probably want: #define CAT_(A,B) A##B #define CAT(A,B) CAT_(A,B) #define GAP 2 #define VERSION CAT(VERSION_WLT_GAP_ , GAP) VERSION //expands to VERSION_WLT_GAP_2 I recommend playing with gcc -E/clang -E a bit, to learn how macros work, before trying to compose anything complex with them.
Well, the answer seems to be the following: // https://stackoverflow.com/questions/5256313/c-c-macro-string-concatenation // Concatenate preprocessor tokens A and B without expanding macro definitions (however, if invoked from a macro, macro arguments are expanded). #define PPCAT_NX(A, B) A ## B // Concatenate preprocessor tokens A and B after macro-expanding them. #define PPCAT(A, B) PPCAT_NX(A, B) // Turn A into a string literal without expanding macro definitions (however, if invoked from a macro, macro arguments are expanded). #define STRINGIZE_NX(A) #A // Turn A into a string literal after macro-expanding it. #define STR(A) STRINGIZE_NX(A) #define COMPLEX_DEPOSITION #ifdef COMPLEX_DEPOSITION #define CD "_COMPDEP" #else #define CD "" #endif #define WIRESLIFETIMES #ifdef WIRESLIFETIMES #define GAP 2 #define WLT STR(PPCAT(_WLT:G, GAP)) #define DISABLE_METROPOLIS #else #define WLT "" #endif #define VERSION VERSIONX CD WLT which produces V008.1-11-g68a9c89cb4-dirty_COMPDEP_WLT:G2 and I am happy with it. Must be noted that I changed -DVERSION=... to -DVERSIONX=... inside Makefile
Construct fixed string by concatenating macro with string
I've went through a number of similar questions and almost got it to work, but not quite. What I have is the standard Macro-Expansion-Stringification-method. #define QUOTEME(M) #M #define DOQUOTE(M) QUOTEME(M) #define XCONCAT(X, Y) X##Y #define CONCAT(X, Y) XCONCAT(X, Y) Then I have a macro PREFIX like this: #define SW_PREFIX XY2Ar- What I was trying to do was: #define SW_FILE DOQUOTE(CONCAT(SW_PREFIX, update)) What this is supposed to output is: "XY2Ar-update" What it outputs on my GCC-type compiler is: error: pasting "-" and "update" does not give a valid preprocessing token Now, I assume that he's replacing the macro correctly, but apparently doesn't want to append update to XY2Ar- because of the -. I also tried: #define SW_FILE DOQUOTE(SW_PREFIX.update) which, once again, almost does what I want, however it outputs XY2Ar-.update, which is not what I want either. I'm out of ideas.
Here is an alternative: #define QUOTEME(M) #M #define COMPOSE(A, B) QUOTEME(A) #B #define SW_PREFIX XY2Ar- #define SW_FILE COMPOSE(SW_PREFIX, update)
Your thinking seems too complicated :-) Do not create a single token to stringify. Simply use string concatenation for separate parts. $ cat x.c #define QUOTEME(M) #M #define DOQUOTE(M) QUOTEME(M) #define SW_PREFIX XY2Ar- #define SW_FILE DOQUOTE(SW_PREFIX) QUOTEME(.update) char *x = SW_FILE; $ gcc -E x.c # 1 "x.c" # 1 "<built-in>" # 1 "<command-line>" # 1 "x.c" char *x = "XY2Ar-" ".update";
Sometimes I keep finding myself forgetting the KISS-principle...and it's times like these where it shows. #define SW_PREFIX "XY2Ar-" #define SW_FILE SW_PREFIX"update" These simple lines, no further expansion or anything return the desired output. As for the reason why it does that: Since there aren't any # in there, it expands SW_PREFIX to "XY2Ar-" and appends "update" to it, which results in "XY2Ar-""update", which, for the compiler, is the same as XY2Ar-update. Thanks to the guy who erased his answers for reminding me.
Concatenate int to string using C Preprocessor
I'm trying to figure out how I can concatenate a #define'd int to a #define'd string using the C Preprocessor. My compiler is GCC 4.1 on CentOS 5. The solution should also work for MinGW. I'd like to append a version number onto a string, but the only way I can get it to work is to make a copy of the version number defines as strings. The closest thing I could find was a method of quoting macro arguments, but it doesn't work for #defines This is does not work. #define MAJOR_VER 2 #define MINOR_VER 6 #define MY_FILE "/home/user/.myapp" #MAJOR_VER #MINOR_VER It doesn't work without the #s either because the values are numbers and it would expand to "/home/user/.myapp" 2 6, which isn't valid C. This does work, but I don't like having copies of the version defines because I do need them as numbers as well. #define MAJOR_VER 2 #define MINOR_VER 6 #define MAJOR_VER_STR "2" #define MINOR_VER_STR "6" #define MY_FILE "/home/user/.myapp" MAJOR_VER_STRING MINOR_VER_STRING
Classical C preprocessor question.... #define STR_HELPER(x) #x #define STR(x) STR_HELPER(x) #define MAJOR_VER 2 #define MINOR_VER 6 #define MY_FILE "/home/user/.myapp" STR(MAJOR_VER) STR(MINOR_VER) The extra level of indirection will allow the preprocessor to expand the macros before they are converted to strings.
A working way is to write MY_FILE as a parametric macro: #define MY_FILE(x,y) "/home..." #x #y EDIT: As noted by "Lindydancer", this solution doesn't expand macros in arguments. A more general solution is: #define MY_FILE_(x,y) "/home..." #x #y #define MY_FILE(x,y) MY_FILE_(x,y)
You can do that with BOOST_PP_STRINGIZE: #define MAJOR_VER 2 #define MINOR_VER 6 #define MY_FILE "/home/user/.myapp" BOOST_PP_STRINGIZE(MAJOR_VER) BOOST_PP_STRINGIZE(MINOR_VER)
How to write a while loop with the C preprocessor?
I am asking this question from an educational/hacking point of view, (I wouldn't really want to code like this). Is it possible to implement a while loop only using C preprocessor directives. I understand that macros cannot be expanded recursively, so how would this be accomplished?
If you want to implement a while loop, you will need to use recursion in the preprocessor. The easiest way to do recursion is to use a deferred expression. A deferred expression is an expression that requires more scans to fully expand: #define EMPTY() #define DEFER(id) id EMPTY() #define OBSTRUCT(id) id DEFER(EMPTY)() #define EXPAND(...) __VA_ARGS__ #define A() 123 A() // Expands to 123 DEFER(A)() // Expands to A () because it requires one more scan to fully expand EXPAND(DEFER(A)()) // Expands to 123, because the EXPAND macro forces another scan Why is this important? Well when a macro is scanned and expanding, it creates a disabling context. This disabling context will cause a token, that refers to the currently expanding macro, to be painted blue. Thus, once its painted blue, the macro will no longer expand. This is why macros don't expand recursively. However, a disabling context only exists during one scan, so by deferring an expansion we can prevent our macros from becoming painted blue. We will just need to apply more scans to the expression. We can do that using this EVAL macro: #define EVAL(...) EVAL1(EVAL1(EVAL1(__VA_ARGS__))) #define EVAL1(...) EVAL2(EVAL2(EVAL2(__VA_ARGS__))) #define EVAL2(...) EVAL3(EVAL3(EVAL3(__VA_ARGS__))) #define EVAL3(...) EVAL4(EVAL4(EVAL4(__VA_ARGS__))) #define EVAL4(...) EVAL5(EVAL5(EVAL5(__VA_ARGS__))) #define EVAL5(...) __VA_ARGS__ Next, we define some operators for doing some logic(such as if, etc): #define CAT(a, ...) PRIMITIVE_CAT(a, __VA_ARGS__) #define PRIMITIVE_CAT(a, ...) a ## __VA_ARGS__ #define CHECK_N(x, n, ...) n #define CHECK(...) CHECK_N(__VA_ARGS__, 0,) #define NOT(x) CHECK(PRIMITIVE_CAT(NOT_, x)) #define NOT_0 ~, 1, #define COMPL(b) PRIMITIVE_CAT(COMPL_, b) #define COMPL_0 1 #define COMPL_1 0 #define BOOL(x) COMPL(NOT(x)) #define IIF(c) PRIMITIVE_CAT(IIF_, c) #define IIF_0(t, ...) __VA_ARGS__ #define IIF_1(t, ...) t #define IF(c) IIF(BOOL(c)) Now with all these macros we can write a recursive WHILE macro. We use a WHILE_INDIRECT macro to refer back to itself recursively. This prevents the macro from being painted blue, since it will expand on a different scan(and using a different disabling context). The WHILE macro takes a predicate macro, an operator macro, and a state(which is the variadic arguments). It keeps applying this operator macro to the state until the predicate macro returns false(which is 0). #define WHILE(pred, op, ...) \ IF(pred(__VA_ARGS__)) \ ( \ OBSTRUCT(WHILE_INDIRECT) () \ ( \ pred, op, op(__VA_ARGS__) \ ), \ __VA_ARGS__ \ ) #define WHILE_INDIRECT() WHILE For demonstration purposes, we are just going to create a predicate that checks when number of arguments are 1: #define NARGS_SEQ(_1,_2,_3,_4,_5,_6,_7,_8,N,...) N #define NARGS(...) NARGS_SEQ(__VA_ARGS__, 8, 7, 6, 5, 4, 3, 2, 1) #define IS_1(x) CHECK(PRIMITIVE_CAT(IS_1_, x)) #define IS_1_1 ~, 1, #define PRED(x, ...) COMPL(IS_1(NARGS(__VA_ARGS__))) Next we create an operator, which we will just concat two tokens. We also create a final operator(called M) that will process the final output: #define OP(x, y, ...) CAT(x, y), __VA_ARGS__ #define M(...) CAT(__VA_ARGS__) Then using the WHILE macro: M(EVAL(WHILE(PRED, OP, x, y, z))) //Expands to xyz Of course, any kind of predicate or operator can be passed to it.
Take a look at the Boost preprocessor library, which allows you to write loops in the preprocessor, and much more.
You use recursive include files. Unfortunately, you can't iterate the loop more than the maximum depth that the preprocessor allows. It turns out that C++ templates are Turing Complete and can be used in similar ways. Check out Generative Programming
I use meta-template programming for this purpose, its fun once you get a hang of it. And very useful at times when used with discretion. Because as mentioned its turing complete, to the point where you can even cause the compiler to get into an infinite loop, or stack-overflow! There is nothing like going to get some coffee just to find your compilation is using up 30+ gigabytes of memory and all the CPU to compile your infinite loop code!
well, not that it's a while loop, but a counter loop, nonetheless the loop is possible in clean CPP (no templates and no C++)
#ifdef pad_always
#define pad(p,f) p##0
#else
#define pad0(p,not_used) p
#define pad1(p,not_used) p##0
#define pad(p,f) pad##f(p,)
#endif
// f - padding flag
// p - prefix so far
// a,b,c - digits
// x - action to invoke
#define n0(p,x)
#define n1(p,x) x(p##1)
#define n2(p,x) n1(p,x) x(p##2)
#define n3(p,x) n2(p,x) x(p##3)
#define n4(p,x) n3(p,x) x(p##4)
#define n5(p,x) n4(p,x) x(p##5)
#define n6(p,x) n5(p,x) x(p##6)
#define n7(p,x) n6(p,x) x(p##7)
#define n8(p,x) n7(p,x) x(p##8)
#define n9(p,x) n8(p,x) x(p##9)
#define n00(f,p,a,x) n##a(pad(p,f),x)
#define n10(f,p,a,x) n00(f,p,9,x) x(p##10) n##a(p##1,x)
#define n20(f,p,a,x) n10(f,p,9,x) x(p##20) n##a(p##2,x)
#define n30(f,p,a,x) n20(f,p,9,x) x(p##30) n##a(p##3,x)
#define n40(f,p,a,x) n30(f,p,9,x) x(p##40) n##a(p##4,x)
#define n50(f,p,a,x) n40(f,p,9,x) x(p##50) n##a(p##5,x)
#define n60(f,p,a,x) n50(f,p,9,x) x(p##60) n##a(p##6,x)
#define n70(f,p,a,x) n60(f,p,9,x) x(p##70) n##a(p##7,x)
#define n80(f,p,a,x) n70(f,p,9,x) x(p##80) n##a(p##8,x)
#define n90(f,p,a,x) n80(f,p,9,x) x(p##90) n##a(p##9,x)
#define n000(f,p,a,b,x) n##a##0(f,pad(p,f),b,x)
#define n100(f,p,a,b,x) n000(f,p,9,9,x) x(p##100) n##a##0(1,p##1,b,x)
#define n200(f,p,a,b,x) n100(f,p,9,9,x) x(p##200) n##a##0(1,p##2,b,x)
#define n300(f,p,a,b,x) n200(f,p,9,9,x) x(p##300) n##a##0(1,p##3,b,x)
#define n400(f,p,a,b,x) n300(f,p,9,9,x) x(p##400) n##a##0(1,p##4,b,x)
#define n500(f,p,a,b,x) n400(f,p,9,9,x) x(p##500) n##a##0(1,p##5,b,x)
#define n600(f,p,a,b,x) n500(f,p,9,9,x) x(p##600) n##a##0(1,p##6,b,x)
#define n700(f,p,a,b,x) n600(f,p,9,9,x) x(p##700) n##a##0(1,p##7,b,x)
#define n800(f,p,a,b,x) n700(f,p,9,9,x) x(p##800) n##a##0(1,p##8,b,x)
#define n900(f,p,a,b,x) n800(f,p,9,9,x) x(p##900) n##a##0(1,p##9,b,x)
#define n0000(f,p,a,b,c,x) n##a##00(f,pad(p,f),b,c,x)
#define n1000(f,p,a,b,c,x) n0000(f,p,9,9,9,x) x(p##1000) n##a##00(1,p##1,b,c,x)
#define n2000(f,p,a,b,c,x) n1000(f,p,9,9,9,x) x(p##2000) n##a##00(1,p##2,b,c,x)
#define n3000(f,p,a,b,c,x) n2000(f,p,9,9,9,x) x(p##3000) n##a##00(1,p##3,b,c,x)
#define n4000(f,p,a,b,c,x) n3000(f,p,9,9,9,x) x(p##4000) n##a##00(1,p##4,b,c,x)
#define n5000(f,p,a,b,c,x) n4000(f,p,9,9,9,x) x(p##5000) n##a##00(1,p##5,b,c,x)
#define n6000(f,p,a,b,c,x) n5000(f,p,9,9,9,x) x(p##6000) n##a##00(1,p##6,b,c,x)
#define n7000(f,p,a,b,c,x) n6000(f,p,9,9,9,x) x(p##7000) n##a##00(1,p##7,b,c,x)
#define n8000(f,p,a,b,c,x) n7000(f,p,9,9,9,x) x(p##8000) n##a##00(1,p##8,b,c,x)
#define n9000(f,p,a,b,c,x) n8000(f,p,9,9,9,x) x(p##9000) n##a##00(1,p##9,b,c,x)
#define n00000(f,p,a,b,c,d,x) n##a##000(f,pad(p,f),b,c,d,x)
#define n10000(f,p,a,b,c,d,x) n00000(f,p,9,9,9,9,x) x(p##10000) n##a##000(1,p##1,b,c,d,x)
#define n20000(f,p,a,b,c,d,x) n10000(f,p,9,9,9,9,x) x(p##20000) n##a##000(1,p##2,b,c,d,x)
#define n30000(f,p,a,b,c,d,x) n20000(f,p,9,9,9,9,x) x(p##30000) n##a##000(1,p##3,b,c,d,x)
#define n40000(f,p,a,b,c,d,x) n30000(f,p,9,9,9,9,x) x(p##40000) n##a##000(1,p##4,b,c,d,x)
#define n50000(f,p,a,b,c,d,x) n40000(f,p,9,9,9,9,x) x(p##50000) n##a##000(1,p##5,b,c,d,x)
#define n60000(f,p,a,b,c,d,x) n50000(f,p,9,9,9,9,x) x(p##60000) n##a##000(1,p##6,b,c,d,x)
#define n70000(f,p,a,b,c,d,x) n60000(f,p,9,9,9,9,x) x(p##70000) n##a##000(1,p##7,b,c,d,x)
#define n80000(f,p,a,b,c,d,x) n70000(f,p,9,9,9,9,x) x(p##80000) n##a##000(1,p##8,b,c,d,x)
#define n90000(f,p,a,b,c,d,x) n80000(f,p,9,9,9,9,x) x(p##90000) n##a##000(1,p##9,b,c,d,x)
#define cycle5(c1,c2,c3,c4,c5,x) n##c1##0000(0,,c2,c3,c4,c5,x)
#define cycle4(c1,c2,c3,c4,x) n##c1##000(0,,c2,c3,c4,x)
#define cycle3(c1,c2,c3,x) n##c1##00(0,,c2,c3,x)
#define cycle2(c1,c2,x) n##c1##0(0,,c2,x)
#define cycle1(c1,x) n##c1(,x)
#define concat(a,b,c) a##b##c
#define ck(arg) a[concat(,arg,-1)]++;
#define SIZEOF(x) (sizeof(x) / sizeof((x)[0]))
void check5(void)
{
int i, a[32769];
for (i = 0; i < SIZEOF(a); i++) a[i]=0;
cycle5(3,2,7,6,9,ck);
for (i = 0; i < SIZEOF(a); i++) if (a[i] != 1) printf("5: [%d] = %d\n", i+1, a[i]);
}
Here's an abuse of the rules that would get it done legally. Write your own C preprocessor. Make it interpret some #pragma directives the way you want.
I found this scheme useful when the compiler got cranky and wouldn't unroll certain loops for me
#define REPEAT20(x) { x;x;x;x;x;x;x;x;x;x;x;x;x;x;x;x;x;x;x;x;}
REPEAT20( val = pleaseconverge(val) );
But IMHO, if you need something much more complicated than that, then you should write your own pre-preprocessor. Your pre-preprocessor could for instance generate an appropriate header file for you, and it is easy enough to include this step in a Makefile to have everything compile smoothly by a single command. I've done it.