CODEWITHSUNDEEP
c
Sato
Sato

Reputation: 8602

Should I manually allocate string ending char '\0' in c?

I'm new to c, and confused by string ending char '\0', should I allocate it?

for example, I want to store a string with a max length of 6;

If I use array, should I use char str[6] or char str[7]?

  char as[3] = "abc";
  printf("%s\n", as);
  //seems no problem

If I use char pointer, should I use char *str = malloc(6) or char *str = malloc(7)?

Upvotes: 2

Views: 118

Answers (3)

Martin Rosenau
Martin Rosenau

Reputation: 18503

In addition to stackptr's answer:

If you are planning to overwrite your array:

char str[30] = "abc";
...
strcpy(str, "Hello world"); /* This will overwrite the content of "str" */

... the length of the array must be the maximum length of the string plus 1.

In the example above you may write strings of up to 29 characters length to the array.

Note that the following definition:

char str[] = "abc";

... implicitly creates an array of 4 characters length so you are limit to 3 characters.

Upvotes: 0

Shrey
Shrey

Reputation: 98

You should be using string length + 1. In your case you must use 7 while declaring the char array. The example you provided would have worked because of the undefined behaviour shown by printf().

Upvotes: 0

lost_in_the_source
lost_in_the_source

Reputation: 11237

For an array that is pre-initialized, you don't need to write a number in the brackets. You can just write

char str[] = "this is my string";

And the compiler will automatically calculate the number of bytes needed.

But for malloc, you must add 1. Ex:

char *strdup(const char *str)
{
    char *ret = malloc(strlen(str) + 1);
    strcpy(ret, str);

    return ret;
}

Upvotes: 3

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