Copying string from source printing strange string of characters [closed] - c

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Im making a lexer and I'm trouble copying a string from my file buffer to the string property of the constructor. Here is the code i'm using to copy a string from the buffer.
static token_t* lexer_str(lexer_t* lexer) {
size_t str_len = 0;
while (true) {
if (lexer->len < 1) {
error_new(lexer->errors, lexer->len, lexer->pos, "Unterminated string.");
return NULL;
} else if (lexer_look(lexer, 0) == '\"') {
lexer_adv(lexer, 1);
break;
} else {
lexer_adv(lexer, 1);
str_len++;
}
}
char* string = malloc(str_len);
for (size_t idx = 0; idx < str_len; idx++)
string[idx] = lexer->src[lexer->ptr - str_len + idx];
token_t* token = token_new(lexer, _str);
token->string = string;
return token;
}
And here is the buffer.
"la la la" "me me me"
and here is the output, the string is coming out as "²²²²\"
Type:0 {
Line: 1
Pos: 0
Number: 10715872
Real: 10715872
String: ²²²²\
}
Why is this happening? Is it just me reading memory from the wrong place. Any help for how I could correctly copy the string into the token would be appricated.

Answer 1

First char* string = malloc(str_len); is too short, and your string is not null terminated after the copy (you copy a buffer given offset and len, the buffer does not contain an ending null char)
change to:
char* string = malloc(str_len+1); // 1 byte more
for (size_t idx = 0; idx < str_len; idx++)
string[idx] = lexer->src[lexer->ptr - str_len + idx];
string[str_len] = '\0'; // don't forget to null-terminate
If the source is, say, empty, then you have a non-null terminated string in string