使用FLex编写SysY词法分析器

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identifier {identifier-nondigit}({identifier-nondigit}|{identifier-digit})*
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identifier-digit [0-9]
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identifier-nondigit [_a-zA-Z]
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br [ \t]+
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%%
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{br} {;}
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"/\*" {
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    printf("<COMMENT>\n");
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    char curr,prev;
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    prev = '\0';
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    curr = input();
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    while(prev!='*'||curr!='/') {prev = curr; curr = input();}
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}
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"//" {
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    printf("<COMMENT>\n");
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    char curr;
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    curr = input();
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    while(curr!='\n') curr = input();
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}
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"int" {printf("<INT>\n");}
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"float" {printf("<FLOAT>\n");}
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"void" {printf("<VOID>\n");}
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"if" {printf("<IF>\n");}
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"else" {printf("<ELSE>\n");}
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"while" {printf("<WHILE>\n");}
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"break"  {printf("<BREAK>\n");}
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"return" {printf("<RETURN>\n");}
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"+"    {printf("<ADD>\n");}
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"-"    {printf("<SUB>\n");}
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"*"    {printf("<MUL>\n");}
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"/"    {printf("<DIV>\n");}
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"%"    {printf("<MOD>\n");}
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"!"    {printf("<NOT>\n");}
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","    {printf("<,>\n");}
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"="    {printf("<=>\n");}
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";"    {printf("<;>\n");}
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">=" {printf("<GE>\n");}
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"<=" {printf("<LE>\n");}
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"==" {printf("<EQ>\n");}
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"!=" {printf("<NE>\n");}
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">" {printf("<GT>\n");}
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"<" {printf("<LT>\n");}
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"||" {printf("<OR>\n");}
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"&&" {printf("<AND>\n");}
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"(" {printf("<(>\n");}
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")" {printf("<)>\n");}
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"[" {printf("<[>\n");}
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"]" {printf("<]>\n");}
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"{" {printf("<{>\n");}
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"}" {printf("<}>\n");}
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\n      { ++yylineno; }
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"0"[0-9a-zA-Z]* {
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    int pos = 1;
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    char c,buf[2];
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    c = yytext[pos++];
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    if (c!='x'&&c!='X'){
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        int total=0;
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        while (c>='0'&&c<='7'){
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            if (c>'9'||c<'0'){
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                printf("Error at Line %d: Invalid characters \'%s\'\n", yylineno, yytext);
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                return -1;
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            }
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            buf[0]=c;
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            buf[1]='\0';
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            total = total*8+atoi(buf);
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            c = yytext[pos++];
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        }
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        if (c!=' '&&c!='\t'&&c!='\n'&&c!='\0'){
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            printf("Error at Line %d: Invalid octalnumber \'%s\'\n", yylineno, yytext);
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            return -1;
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        }
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        printf("<INTNUM, %d>\n", total);
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        return 1;
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    } else {
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        c = yytext[pos++];
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        int total = 0;
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        while ((c>='0'&&c<='9')||(c>='a'&&c<='f')||(c>='A'&&c<='F')){
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            if (c>='0'&&c<='9'){
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                total = total*16 + c-'0';
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            }
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            if (c>='a'&&c<='f'){
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                total = total*16 + c-'a'+10;
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            }
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            if (c>='A'&&c<='F'){
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                total = total*16 + c-'A'+10;
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            }
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            c = yytext[pos++];
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        }
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        if (c!=' '&&c!='\t'&&c!='\n'&&c!='\0'){
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            printf("Error at Line %d: Invalid hex number \'%s\'\n", yylineno, yytext);
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            return -1;
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        }
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        printf("<INTNUM, %d>\n", total);
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    }
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}
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{identifier} {return IDENTIFIER;}
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[0-9]+ {printf("<INTNUM, %d>\n",atoi(yytext));}
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. { printf("Error at Line %d: Invalid characters \'%s\'\n", yylineno, yytext);
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 }
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%%
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int main(int argc, char** argv) {
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    if (argc > 1) {
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        yyin = fopen(argv[1], "r");
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        if (!yyin) {
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            perror("Error opening file");
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            return 1;
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        }
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    } else {
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        printf("Usage: %s <filename>\n", argv[0]);
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        return 1;
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    }
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    while (yylex() != 0);
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    fclose(yyin);  // Remember to close the file when done
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    return 0;
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}
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int yywrap() {
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    return 1;
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}