CODEWITHSUNDEEP
cpointerssubstring
user983567
user983567

Reputation: 27

Substrings in C

Given I have declared:

char **string;

How do I pass it into another function with a substring starting at a certain position?

I currently have it as:

function((*string)[pos])

intending it to be a substring that begins at position pos. Any advice?

Upvotes: 0

Views: 227

Answers (5)

paxdiablo
paxdiablo

Reputation: 881363

There are two ways I know of to do this. Both of them require a char* so the string you're working with is *string in your case (string is the pointer to the char* representing the string, so you have to dereference it to get the actual string).

The first is simple pointer addition, as in (*string) + 7. This gives you the string starting at the eighth character.

The second is to get the address of the starting character, as in &((*string)[7]).

Both of these will only "work" if you're string is at least eighth characters long. In other words, don't try to look beyond the end of the string.

Upvotes: 0

nickb
nickb

Reputation: 59699

You could pass the pointer of the whole string to the function along with an integer length, which the function will take into consideration in its logic.

Or, you can extract a specific substring (assuming you want to only trim characters off the front of the string) by using pointer arithmetic:

char * x = "Some text";
char * y;
y = x + 5;

Now, y is pointing to the string "text". http://codepad.org/icVjE6in

Or, extracting a substring with a specific start and end would require using that and strncpy.

Upvotes: 0

Andrejs Cainikovs
Andrejs Cainikovs

Reputation: 28434

char **string;
function((*string) + pos)

or

char *string;
function(string + pos)

Upvotes: 1

harald
harald

Reputation: 6126

(*string)[pos] denotes the char at position pos. You probably want (*string) + pos instead.

Upvotes: 0

Jeff Mercado
Jeff Mercado

Reputation: 134841

The type of string is char **.

string is of type char **. (pointer to your string)
*string is of type char *. (the string itself)
**string is of type char. (a letter in the string)

So you want to offset into the string itself:

(*string) + pos

which will have type char *.

Upvotes: 1

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