Difference Between two code snippets?

[rraagg]

Hi I'm trying to workout the difference in behaviour of the following to code snippets

This one Works:

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])
{
	const char *words[4] = { "aardvark", "abacus", 
							 "allude", "zygote" };
	int wordCount = 4;
	
	int i;
	for (i = 0; i < wordCount; i++) {
		NSLog (@"%s is %d characters long",
			   words[i], strlen(words[i]));
	}
	
	return (0);
	
} // main

This doesnt:

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])
{
	const char words[4] = { "aardvark", "abacus", 
							 "allude", "zygote" };
	int wordCount = 4;
	
	int i;
	for (i = 0; i < wordCount; i++) {
		NSLog (@"%s is %d characters long",
			   words[i], strlen(words[i]));
	}
	
	return (0);
	
} // main

The difference is const char words[4] decleration.

Am I right in thinking

const char *words[4]

works because it returns the address of the first array element and the list can then be assigned because it knows the starting adress from the pointer?

and

const char words[4]

doesnt work because it thinks your trying to assign the array list to the fourth element which is not big enought?

[FlyingDiver]

The first is an array of 4 pointers to chars (ie, C-string pointers). The second is an array of 4 chars (which isn't much at all).

joe

[rraagg]

so when a char is not declared as a char[4] it can be of any size ie almost like a string variable ie char on its one is not 1 byte long?

[FlyingDiver]

Originally Posted by rraagg

so when a char is not declared as a char[4] it can be of any size ie almost like a string variable ie char on its one is not 1 byte long?

char foo - one char (one byte)
char *foo - a pointer (4 or 8 bytes)
char foo[4] - four chars (4 bytes)
char *foo[4] - an array of 4 char pointers (16 or 32 bytes)

joe

[rraagg]

Thanks for the example Joe.
So these are the restrictions:
char foo - one char (one byte)
foo = "a";
char *foo - a pointer (4 or 8 bytes)
foo can only = &testchar ...this is where i get confused. Can *foo store anything(eg string) up to 8bytes long or can it just store a 4 to 8byte address
char foo[4] - four chars (4 bytes)
foo[1] = "r"; etc
char *foo[4] - an array of 4 char pointers (16 or 32 bytes)
so basically i can store four addresses for chars eg &testchar

[FlyingDiver]

Originally Posted by rraagg

char *foo - a pointer (4 or 8 bytes)
foo can only = &testchar ...this is where i get confused. Can *foo store anything(eg string) up to 8bytes long or can it just store a 4 to 8byte address
char foo[4] - four chars (4 bytes)
[/b][/i]

While you could probably make a pointer store something else, you'll have to fool the compiler to do it without generating warnings. That is, you can probably do:

char *foo = 'abcd';

But doing so will generate a warning about "incompatible types".

joe