%{

#define YYERROR_VERBOSE 1

int column = 1; 

extern int yylval;

static int next_column = 1;

#define HANDLE_COLUMN column = next_column; next_column += strlen(yytext)

std::string line;

size_t consumed = 0;

size_t available = 0;

char ch;

size_t min(size_t a, size_t b);

#define YY_INPUT(buf, result, max_size) {\

    if (available <= 0) {\

        consumed = 0;\

        if (std::getline(yyin, line)) {\

          if (!yyin.eof()) {\

            line += '\n';\

          }\

          available = line.length();\

        } else {\

            available = 0;\

        }\

    }\

    result = min(available, max_size);\

    std::strncpy(buf, line.c_str() + consumed, result);\

    consumed += result;\

    available -= result;\

}

%}

%option c++ noyywrap noinput nounput yylineno

%%

[\t ]+   { HANDLE_COLUMN; }  // 每个规则都需要添加 HANDLE_COLUMN;

[0-9]+   { HANDLE_COLUMN; yylval = atoi(yytext);  return NUM; } // 添加 HANDLE_COLUMN; 后跟原本规则对应的动作即可

\n       { HANDLE_COLUMN; next_column = 1; } //next_column = 1 因为换行了，“下一个列” 在新行中从 1 开始

.        { HANDLE_COLUMN; return yytext[0]; }

%%

size_t min(size_t a, size_t b) {

    return b < a ? b : a;

}

%{

/**

 * There is a little bug in bison 3.8 that causes a [set but not used] 

 * warning to be emitted on the line below:

 *

 * [build] parser.cc:434:9: warning: variable 'yynerrs_' set but not used [-Wunused-but-set-variable]

 * [build]   434 |     int yynerrs_ = 0;

 * [build]       |         ^

 * 

 * This is a known issue and it has been fixed.

 * Patches: https://mail.gnu.org/archive/html/bison-patches/2022-08/msg00006.html

 */

#pragma GCC diagnostic ignored "-Wunused-but-set-variable"

#define YYERROR_VERBOSE 1

extern int column;

extern std::string line;

%}

%%

    // some rules

%%

void yy::parser::error(const std::string& msg)

{

  std::cerr << "error: " << msg << " in line " << lexer.lineno() << ", column " << column << std::endl;

  std::cerr << line;

  // Print underscores to mark the error position

  for (int i = 0; i < column - 1; ++i)

    std::cerr << "_";

  std::cerr << "^" << std::endl;

}