Thread: How come this works perfectly? Replacing a 2d character array with 1d array.

Well it doesn't, unless you follow up with something like

names[0] = malloc(100);

Then you can write up to 99 chars into the memory that names[0] points to.

If you do that for all the pointers, you've effectively created
char names[5][100];

But if you DON'T do these things, then your "friend" is playing with fire, and it's only a matter of time before it all goes so horribly wrong.

> It worked! I saw it!
Yes, so have I, many times.
It doesn't make you a good programmer though, just a lucky one.

> I was wondering how is this even possible
Nothing more than pure dumb luck.

Hey, it's your exam - put what you like and see what happens.

Originally Posted by matthayzon89

[...]its normal for one to think to use a 2d array [...]
A programmer that I know showed me that this can be done with a 1d array [...]

Code:

char* names[5];

Well, what you see there is 5 element array of pointers to char, which effectively can make 2d char array, but you have to allocate memory for every char* element, or you won't be using it properly. (Also, you can allocate different amounts of memory for each element - see argv?)

It's not that different from char** names or char names[][] if you think about it (yes, I'm simplifying a bit).

If your friend is not allocating memory properly, I can't see how the program would even work consistently, without a segfault from time to time (or all the time). So he did, but you didn't see where and how, or he didn't and had a dumb luck, like Salem said.

Originally Posted by matthayzon89

[...]and he can access an entire string in 1 position in the character array which makes no sense to me.

So you see, you're mistaken, its not that he can access entire string in 1 position of the char[] - because it's not char[], it's char* [] - not a char array, but array of pointers to char - you could say, array of c-strings. Now does it make sense?

Originally Posted by matthayzon89

[...]You explanation which is "Nothing more than pure dumb luck" translates to "I dont know why it works".....

I know it wasn't pointed against me, but let me answer.
I'm sure Salem has far more knowledge on C and internals than I do, but I think I have some idea why that can sometimes work.
You see, when you create new array of pointers to char, you get the memory for that array, that memory has some "random" values that were there before, unless you initialize the array to some values.
Now, these values are interpreted as pointers to char, and they coincidently may point to "valid" places in memory. If you write to that pointed memory, you can end up crashing your program, but you may also get lucky, and not crash it. The point is, even if it works at times, you have absolutely no guarantee that it will work the next time you run your application. It could even break your application silently, overwriting other variables' memory, while you think everything is in perfect order.
All kinds of stuff could happen.

Hopefully someone will correct me if I'm wrong.

Who cares "why" it works when it's wrong?

Yes, if you posted the exact code, I could probably give you a plausible (and contrived) answer as to why it works IN THAT SPECIFIC CASE.

But it isn't any knowledge that will do you any good in future. You couldn't take it and apply it to all your programs and have success every time.

I'm only interested in showing you how to do it right, not explain myriads of exceptional "well it works for me bub" programs which are plainly wrong to all but the author.

If you don't want to learn, just listen to your "friend" and stop posting.

Originally Posted by matthayzon89

A programmer that I know showed me that this can be done with a 1d array, how is this possible?

That said, this really can be done with a 1D array of char: you simply manually break up the one long array into parts.

Originally Posted by Salem

If you don't want to learn, just listen to your "friend" and stop posting.

If you read my older post on this thread you would see that I am asking because I DO want to learn. I know my friend is wrong, like i said earlier in my other posts and I am not planning on using this. I was simply curious to WHY it works.

Why do you even bother replying ......?

..... What does "it works because of 'dumb luck' " teach me about why c programming compiles the code with no errors? NOTHING.

If your 'teaching methods' involves being a jerk towards me, when I ask a completely reasonable question, than I have no interest in learning anything from you.

Originally Posted by matthayzon89

So, once it breaks it up into parts, how is it successful in accessing a whole string via 1 array slot?

Perhaps an example will illustrate the idea:

Code:

#include <string.h>
#include <stdio.h>

int main(void)
{
    char strings[12];
    strcpy(&strings[0], "hello");
    strcpy(&strings[6], "world");
    printf("%s\n%s\n", &strings[0], &strings[6]);
    return 0;
}

Of course, this is quite silly, but it does have a sensible practical application: maybe you want a dynamic 2D array. You could have a dynamic array of pointers, and then allocate a dynamic array for each pointer. Or, you could allocate one big dynamic array, and then allocate another dynamic array of pointers, and then get those pointers to point to the parts of this one big dynamic array, and thus be able to access it as if it were a "normal" 2D array. Ultimately, a "normal" fixed size 2D array is also one fixed size array that the compiler has divided for you.

Until you post some actual code from your "friend" which apparently works for them, then there ain't much anyone here can do to help you figure it out.

And I mean an actual "working" program, not a 1-line declaration and a random bunch of words sounding like they were plucked straight from the ass of some politician.