CODEWITHSUNDEEP
cc-stringsnull-terminatednul
Rômulo M. Farias
Rômulo M. Farias

Reputation: 1523

*char ending with double '\0'

My code is crashing because of a lack of the char '\0' at the end of some strings.

It's pretty clear to me why we have to use this termination char. My question is, is there a problem adding a potential 2nd null character to a character array - to solve string problems?

I think it's cheaper just add a '\0' to every string than verify if it needs and then add it, but I don't know if it's a good thing to do.

Upvotes: 2

Views: 396

Answers (3)

chux
chux

Reputation: 154280

is there a problem to have this char ('\0') twice at the end of a string?

This question lacks clarity as "string" means different things to people.
Let us use the C specification definition as this is a C post.

A string is a contiguous sequence of characters terminated by and including the first null character. C11 §7.1.1 1

So a string, cannot have 2 null characters as the string ends upon reaching its first one. @Michael Walz

Instead, re-parse to "is there a problem adding a potential 2nd null character to a character array - to solve string problems?"

A problem with attempting to add a null character to a string is confusion. The str...() functions work with C strings as defined above. 

// If str1 was not a string, strcpy(str1, anything) would be undefined behavior.
strcpy(str1, "\0");  // no change to str1

char str2[] = "abc";
str2[strlen(str2)] = '\0'; // OK but only, re-assigns the \0 to a \0
// attempt to add another \0
str2[strlen(str2)+1] = '\0'; // Bad: assigning outside `str2[]` as the array is too small

char str3[10] = "abc";
str3[strlen(str3)+1] = '\0'; // OK, in this case
puts(str3);                  // Adding that \0 served no purpose

As many have commented, adding a spare '\0' is not directly attending the code's fundamental problem. @Haris @Malcolm McLean

That unposted code is the real issue that need solving @Yunnosch, and not by attempting to append a second '\0'.

Upvotes: 5

ilkkachu
ilkkachu

Reputation: 6537

I think it's cheaper just add a '\0' to every string than verify if it needs and then add it, but I don't know if it's a good thing to do.

Where would you add it? Let's assume we've done something like this:

char *p = malloc(32);

Now, if we know the allocated length, we could put a '\0' as the last character of the allocated area, as in p[31] = '\0'. But we don't how long the contents of the string are supposed to be. If there's supposed to be just foobar, then there'd still be 25 bytes of garbage, which might cause other issues if processed or printed.

Let alone the fact that if all you have is the pointer to the string, it's hard to know the length of the allocated area.

Probably better to fix the places where you build the strings to do it correctly.

Upvotes: 3

Haris
Haris

Reputation: 12272

Having '\0' is not a problem, unless you have not gone out of bounds of that char array.

You do have to understand that, having '\0' twice would mean, any string operation would not even know that there is a second '\0'. They will just read till the first '\0', and be with it. For them, the first '\0' is the Null terminating character and there should not be anything after that.

Upvotes: 2

Related Questions