BOOST_PP_SEQ_ENUM with single quotes?

Question

Basically I want to split single token to multiple tokens enclosed in single quotes but as this seems impossible I've stopped on this. Basically:

#include <boost/preprocessor/seq/enum.hpp>

char string[] = {BOOST_PP_SEQ_ENUM((F)(l)(y)(O)(f)(f)(L)(e)(d)(g)(e))};

However how could I add the single quotes in?

It is possible to split string literal into separate chars at compiler time without any macros. — user7860670, Feb 16 '19 at 17:26

Justin · Answer 1 · 2019-02-16T17:42:51.127

I don't believe it's possible to create character literals in standard compliant C, see C preprocessor: How to create a character literal? .

However, if you just want characters, you do have a few options:

You can expand it to a string literal with BOOST_PP_STRINGIZE and BOOST_PP_SEQ_CAT:

char string[] = BOOST_PP_STRINGIZE(
    BOOST_PP_SEQ_CAT((F)(l)(y)(O)(f)(f)(L)(e)(d)(g)(e)));
// Equivalent to:
char string2[] = "FlyOffLedge";

Live on Godbolt

You can expand each character to "c"[0]:

#define TO_CSV_CHARS_OP(s, data, elem) BOOST_PP_STRINGIZE(elem)[0]
#define TO_CSV_CHARS(seq) \
    BOOST_PP_SEQ_ENUM(BOOST_PP_SEQ_TRANSFORM(TO_CSV_CHARS_OP, , seq))

char string[] = {
    TO_CSV_CHARS((F)(l)(y)(O)(f)(f)(L)(e)(d)(g)(e))
};
// Equivalent to:
char string2[] = {
    "F"[0],
    "l"[0],
    "y"[0],
    "O"[0],
    "f"[0],
    "f"[0],
    "L"[0],
    "e"[0],
    "d"[0],
    "g"[0],
    "e"[0]
};

Live on Godbolt

score 1 · Answer 2 · answered Feb 16 '19 at 17:56

You can adapt this answer in the linked question to C pretty easily to accomplish the original goal (live example):

#include <boost/preprocessor/repetition/repeat.hpp>
#include <boost/preprocessor/punctuation/comma_if.hpp>

#define GET_CH(s, i) ((i) >= sizeof(s) ? '\0' : (s)[i])

#define STRING_TO_CHARS_EXTRACT(z, n, data) \
        BOOST_PP_COMMA_IF(n) GET_CH(data, n)

#define STRING_TO_CHARS(STRLEN, STR)  \
        BOOST_PP_REPEAT(STRLEN, STRING_TO_CHARS_EXTRACT, STR)

char string[] = {STRING_TO_CHARS(12, "FlyOffLedge")};

I don't think it's possible in C to handle the length automatically.

If all you're after is the question as asked, you can use a trick like in Justin's answer to get the first character of each stringized character without using character literal syntax (similar live example).

BOOST_PP_SEQ_ENUM with single quotes?

2 Answers2