lexicalAnalyzerGenerator.lex

%{
 #include<string.h>
 int line_number=0;
 int line_position=0;
 void print_message(char*,char*,int,int);
 void print_error(char*,int,int);
%}
comments \/\/.*
letter [A-Za-z]
delim [ \t]
delims {delim}+
digit [0-9]
intnumber {digit}+
exponent (E|e)(\+|\-)?{digit}+
fraction \.{digit}+
realnumber ({digit}+{exponent})|({digit}+{fraction}({exponent}?))
ws {delim}+
id {letter}({letter}|{digit})*
keyword int|real|if|then|else|while

%%

\n {line_position=0;line_number++;}
{delims} {line_position+=yyleng;}
{comments} {/* No actions on comments */}
{keyword} {print_message("KEYWORD",yytext,line_number,line_position);line_position+=yyleng;}
"{" {print_message("DELIMITER","LEFT_BRACES",line_number,line_position);line_position+=yyleng;}
"}" {print_message("DELIMITER","RIGHT_BRACES",line_number,line_position);line_position+=yyleng;}
"(" {print_message("DELIMITER","LEFT_PARENTHESIS",line_number,line_position);line_position+=yyleng;}
")" {print_message("DELIMITER","RIGHT_PARENTHESIS",line_number,line_position);line_position+=yyleng;}
";" {print_message("DELIMITER","SEMICOLON",line_number,line_position);line_position+=yyleng;}
"," {print_message("DELIMITER","COMMA",line_number,line_position);line_position+=yyleng;}
{id} {print_message("ID",yytext,line_number,line_position);line_position+=yyleng;}
{intnumber} {int num_len = yyleng;if(num_len>0 && num_len<=10 && (num_len<10 || strcmp(yytext,"2147483648")<0)){print_message("INTNUMBER",yytext,line_number,line_position);line_position+=yyleng;}else{print_error("Number format error",line_number,line_position);exit(1);}}
{realnumber} {char* p = strchr(yytext,'e');if(p==NULL)p=strchr(yytext,'E');if(p!=NULL){int ex = atoi(1+p);if(ex>128||ex<-128){print_error("Absolute value of exponent must not more than 128",line_number,line_position);exit(1);}}print_message("REAL_NUMBER",yytext,line_number,line_position);line_position+=yyleng;} 
"+" {print_message("OPERATOR","ADD",line_number,line_position);line_position+=yyleng;}
"-" {print_message("OPERATOR","SUB",line_number,line_position);line_position+=yyleng;}
"*" {print_message("OPERATOR","MUL",line_number,line_position);line_position+=yyleng;}
"/" {print_message("OPERATOR","DIV",line_number,line_position);line_position+=yyleng;}
"=" {print_message("OPERATOR","ASSIGN",line_number,line_position);line_position+=yyleng;}
"==" {print_message("OPERATOR","EQ",line_number,line_position);line_position+=yyleng;}
"<" {print_message("OPERATOR","LT",line_number,line_position);line_position+=yyleng;}
">" {print_message("OPERATOR","GT",line_number,line_position);line_position+=yyleng;}
"<=" {print_message("OPERATOR","LE",line_number,line_position);line_position+=yyleng;}
">=" {print_message("OPERATOR","GE",line_number,line_position);line_position+=yyleng;}
"!=" {print_message("OPERATOR","NE",line_number,line_position);line_position+=yyleng;}
. {char* a=(char*)malloc(sizeof(char)*(20+yyleng));strcpy(a,"Exception character \"");print_error(strcat(strcat(a,yytext),"\""),line_number,line_position);free(a);exit(1);}

%%

int main(){
	yylex();
	return 0;
}

void print_message(char* token_type,char* attribute_value,int line_number,int line_position){
	printf("%s\t\t%s\t\t%d\t\t%d\n",token_type,attribute_value,line_number,line_position);
}

void print_error(char* message,int line_number,int line_position){
	fprintf(stderr,"ERROR: %s. In line %d, position %d.\n",message,line_number,line_position);
}

int yywrap(){
	return 1;
}