“--input custom” examples

bool lex (const char * cursor, const char * const limit)
{
    const char * marker;
    const char * ctxmarker;
#   define YYCTYPE        char
#   define YYPEEK()       *cursor
#   define YYSKIP()       ++cursor
#   define YYBACKUP()     marker = cursor
#   define YYBACKUPCTX()  ctxmarker = cursor
#   define YYRESTORE()    cursor = marker
#   define YYRESTORECTX() cursor = ctxmarker
#   define YYLESSTHAN(n)  limit - cursor < n
#   define YYFILL(n)      {}
    /*!re2c
        "int buffer " / "[" [0-9]+ "]" { return true; }
        *                              { return false; }
    */
}

int main ()
{
    const char buffer [] = "int buffer [1024]";
    return !lex (buffer, buffer + sizeof (buffer));
}

#include <sstream>

bool lex (std::istringstream & is, const std::streampos limit)
{
    std::streampos marker;
    std::streampos ctxmarker;
#   define YYCTYPE        char
#   define YYPEEK()       is.peek ()
#   define YYSKIP()       is.ignore ()
#   define YYBACKUP()     marker = is.tellg ()
#   define YYBACKUPCTX()  ctxmarker = is.tellg ()
#   define YYRESTORE()    is.seekg (marker)
#   define YYRESTORECTX() is.seekg (ctxmarker)
#   define YYLESSTHAN(n)  limit - is.tellg () < n
#   define YYFILL(n)      {}
    /*!re2c
        "int buffer " / "[" [0-9]+ "]" { return true; }
        *                              { return false; }
    */
}

int main ()
{
    const char buffer [] = "int buffer [1024]";
    std::istringstream is (buffer);
    return !lex (is, sizeof (buffer));
}

#include <stdio.h>

char peek (FILE * f)
{
    char c = fgetc (f);
    ungetc (c, f);
    return c;
}

bool lex (FILE * f, const long limit)
{
    long marker;
    long ctxmarker;
#   define YYCTYPE        char
#   define YYPEEK()       peek (f)
#   define YYSKIP()       fgetc (f)
#   define YYBACKUP()     marker = ftell (f)
#   define YYBACKUPCTX()  ctxmarker = ftell (f)
#   define YYRESTORE()    fseek (f, marker, SEEK_SET)
#   define YYRESTORECTX() fseek (f, ctxmarker, SEEK_SET)
#   define YYLESSTHAN(n)  limit - ftell (f) < n
#   define YYFILL(n)      {}
    /*!re2c
        "int buffer " / "[" [0-9]+ "]" { return true; }
        *                              { return false; }
    */
}

int main ()
{
    const char buffer [] = "int buffer [1024]";
    const char fn [] = "input.txt";

    FILE * f = fopen (fn, "w");
    fwrite (buffer, 1, sizeof (buffer), f);
    fclose (f);

    f = fopen (fn, "rb");
    int result = !lex (f, sizeof (buffer));
    fclose (f);

    return result;
}