// re2c $INPUT -o $OUTPUT
#include <assert.h>
#include <stddef.h>

struct SemVer { int major, minor, patch; };

static int s2n(const char *s, const char *e) { // pre-parsed string to number
    int n = 0;
    for (; s < e; ++s) n = n * 10 + (*s - '0');
    return n;
}

static bool lex(const char *str, SemVer &ver) {
    const char *YYCURSOR = str, *YYMARKER;

    // User-defined tag variables that are available in semantic action.
    const char *t1, *t2, *t3, *t4, *t5;

    // Autogenerated tag variables used by the lexer to track tag values.
    /*!stags:re2c format = 'const char *@@;\n'; */

    /*!re2c
        re2c:yyfill:enable = 0;
        re2c:define:YYCTYPE = char;
        re2c:tags = 1;

        num = [0-9]+;

        @t1 num @t2 "." @t3 num @t4 ("." @t5 num)? [\x00] {
            ver.major = s2n(t1, t2);
            ver.minor = s2n(t3, t4);
            ver.patch = t5 != NULL ? s2n(t5, YYCURSOR - 1) : 0;
            return true;
        }
        * { return false; }
    */
}

int main() {
    SemVer v;
    assert(lex("23.34", v) && v.major == 23 && v.minor == 34 && v.patch == 0);
    assert(lex("1.2.999", v) && v.major == 1 && v.minor == 2 && v.patch == 999);
    assert(!lex("1.a", v));
    return 0;
}