CODEWITHSUNDEEP
c
Doug Smith
Doug Smith

Reputation: 29326

What does this block of C code do in order to find the end character?

char *start = str;
char *end = start + strlen(str) - 1; /* -1 for \0 */
char temp;

How does that find the end of the string? If the string is giraffe, start holds that string, then you have:

char *end = "giraffe" + 7 - 1;

How does that give you the last char in giraffe? (e)

Upvotes: 0

Views: 87

Answers (4)

John Kugelman
John Kugelman

Reputation: 361917

Here's how "giraffe" is laid out in memory, with each number giving that character's index.

g i r a f f e \0
0 1 2 3 4 5 6 7

The last character e is at index 6. str + 6, alternatively written as &str[6], yields address of the last character. This is the address of the last character, not the character itself. To get the character you need to dereference that address, so *(str + 6) or str[6] (add a *, or remove the &).

In English, here are various ways to access parts of the string:

 str ==   str + 0  == &str[0]        address of character at index 0
     ==   str + 6  == &str[6]        address of character at index 6
*str == *(str + 0) ==  str[0]        character at index 0 ('g')
     == *(str + 6) ==  str[6]        character at index 6 ('e')

Upvotes: 8

Ivy Gorven
Ivy Gorven

Reputation: 155

There is no string type in C, just char, and arrays of char.

I would tell you to google "c strings", but since that's apparently a term that you need safesearch for these days, here's a link: http://www.cprogramming.com/tutorial/lesson9.html

Upvotes: 1

Paul
Paul

Reputation: 141887

If the string is giraffe, start holds that string

Not exactly, start is a char *, so it holds a pointer, not a string. It points to the first character of "giraffe": g.

start + 1 is also a char * pointer and it points to the next element of size char, in this case the i.

start + 5 is a pointer to the second f.

start + 6 is a pointer to the e.

start + 7 is a pointer to the special character \0 or NUL, which denotes the end of a string in C.

Upvotes: 3

Joshjje
Joshjje

Reputation: 220

start is a pointer to the string "giraffe" in memory, not the string itself.

Likewise end is a pointer to the start of the string + 7 bytes (minus one to account for the null terminator).

Upvotes: 2

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