Return empty string in c

Question

In my function I want to return an empty string "", function looks like this:

char *myFunction(nodeType *arg){
   if (something){
      return anotherFunction(arg);
   } else {
      return EMPTYSTRING;
   }
}

(EMPTYSTRING should be replaced with correct expression to return "")

Some ways I came up with:

return ""

return '\0'

What is the right way to return an empty string?

'\0' is not correct. That's not a char *. You're returning null, not an empty string. — Millie Smith
– Millie Smith, Commented Oct 1, 2017 at 17:58
I can't return NULL, because later I concatenate returned values, so it will be worse implementation, if I have to check every returned values for NULL — Misho Tek
– Misho Tek, Commented Oct 1, 2017 at 18:00
If you don't return null, you're going to have to malloc every time you return an empty string because you're returning char * and not const char *. Just something to be aware of. return "" will give you read-only memory that shouldn't be freed. — Millie Smith
– Millie Smith, Commented Oct 1, 2017 at 18:02

Adem · Accepted Answer · 2017-10-01 18:00:38Z

9

It is not good idea to return "". Because, it is const char and you may try to dealloc it in where you get it from the function and this likely crashes your application.

So, I would return strdup(""), so you can free it safely.

answered Oct 1, 2017 at 18:00

Adem

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2 Comments

Artemy Vysotsky Over a year ago

I would not assume anotherFunction allocated memory without seeing a code

Millie Smith Over a year ago

@ArtemyVysotsky I assumed that anotherFunction allocates memory because the return type is char * and not const char *. Though I concede it's entirely possible they're just using the wrong return type. @OP, make sure to free the string returned from strdup.

Basya · Accepted Answer · 2017-10-01 18:01:15Z

3

return '\0' is not correct; it is a null character.

return "";

is more correct.

And you can make a small test function to test returning an empty string, before your data structure is implemented.

answered Oct 1, 2017 at 18:01

Basya

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Comments

Antti Haapala · Accepted Answer · 2017-10-01 18:49:43Z

3

\0 is indeed a null-pointer constant, not an empty string, so returning that would still return a null pointer.

However you've got another problem here.

If anotherFunction returns a string that you don't need to free() then it is correct to return "" here. If it returns a dynamically malloc()ated string that you must free(), then you also need to return a dynamically allocated empty string here - return calloc(1, 1); would do the trick.

answered Oct 1, 2017 at 18:49

Antti Haapala

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