CODEWITHSUNDEEP
clex
yildizabdullah
yildizabdullah

Reputation: 1981

lex - how to eliminate double quotes from a string literal

I want to eliminate double quotes which are at the beginning and end of a string.

I take a string literal from my input file using a Lex rule as follows:

\".*\"   {yyno++; yylval.string = strdup(yytext); return STRINGLITERAL;}

But when I use a string somewhere in Yacc program, I want to use only the string part.

Could you help me with this?

Upvotes: 0

Views: 3716

Answers (2)

user3023293
user3023293

Reputation: 11

\".*\" {
    yylval.string = (char*)calloc(strlen(yytext)-1, sizeof(char));
    strncpy(yylval.string, &yytext[1], strlen(yytext)-2);
    return STRINGLITERAL;
}

Jan explained it well, I'm just clarifying the lex and fixing a few typos for the next poor soul.

Upvotes: 1

Jack
Jack

Reputation: 133669

You just need to take the relevant part, eg:

 // you allocate a string which is the length of the token - 2 " + 1 for '\0'
 yylval.string = calloc(strlen(yytext)-1, sizeof(char));
 // you copy the string
 strncpy(yylval.string, &yytext[1], strlen(yytext-2));
 // you set the NULL terminating at the end
 yylval.string[yytext-1] = '\0';

So that if yytext == "\"foobar\"" first you allocate a string of length 8 - 2 + 1 = 7 bytes (which is correct since it will be foobar\0, then you copy 8 - 2 characters starting from 'f', finally you set the NULL terminating character.

Actually with calloc memory is already set to 0 so you don't need to place the NULL terminating character but with malloc you would.

Upvotes: 2

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