Passing char[][] as argument

[krreks]

I'm trying to pass this array

char files[num][maxLen+8];

like this

if(fillFileArr(&(files[0][0]), &(buf[0]), num)==-1)
	return -1;

to this function

int fillFileArr(char ** files, char * buf, int num) {
	int word=0, wordPos=0, bufferPos=0;
	while(word<num && buf[bufferPos]!='\0') {
		if(word==0 && wordPos==0 && bufferPos==0)
			printf("! ");
		if(buf[bufferPos]=='\n') {
			if(buf[bufferPos+1]!='\0')
				printf("\n! ");
		
		
			word++;
			wordPos=0;
		} else {
			printf("files[%d][%d] = %c\n", word, wordPos, buf[bufferPos]);
			files[word][wordPos++] = buf[bufferPos];
			printf("%c",buf[bufferPos]);
		}
		bufferPos++;
	}
	return 0;
}

but it results in a seg fault... I guess there's a pointer mistake somewhere, but can't really find it..

Would someone please point it out?

Thanks in advance

[Banfa]

&(files[0][0]) has type char *

but

int fillFileArr(cha r ** files, char * buf, int num)

is a function expecting char **. Actually I am rather surprised that this doesn't actually produce any compiler warnings.

Also files[word][wordPos++] = buf[bufferPos]; is trying to pretend that files inside the function is still a char [][] but it isn't.

Is maxLen fixed? (i.e. a constant) if so you could try

int fillFileArr(cha r (*files)[maxLen+8], char * buf, int num)

otherwise you probably need to pass in a char * and the 2 dimensions of the array pointed to.

[arnaudk]

if(fillFileArr( &(files[0][0]), &(buf[0]), num)==-1) is wrong: is &(files[0][0]) of type char ** ? I suggest you read this.
EDIT: Oops, Banfa was faster.

[weaknessforcats]

It probably here:

if(fillFileArr(&(files[0][0]), &(buf[0]), num)==-1) 
    return -1;

Your function needs a char** and you have provided a char*.

And I would like to know what compiler you are using as your code does not compile. My compiler complains about &files[0][0] not being a char**.

Also, your function parameter for this array is not a char**. A char** is not the address of an array. In your case the array is:

char files[num][maxLen+8];

so the function argument has to be a pointer to an array of maxLen+8:

int fillFileArr(char (* files)[maxLen+8], char * buf, int num) { 
etc...

Read this: http://bytes.com/forum/thread772412.html.

[krreks]

It probably here:

if(fillFileArr(&(files[0][0]), &(buf[0]), num)==-1) 
    return -1;

Your function needs a char** and you have provided a char*.

Ok

And I would like to know what compiler you are using as your code does not compile. My compiler complains about &files[0][0] not being a char**.

gcc/cc in Xcode for OSX Leopard

Also, your function parameter for this array is not a char**. A char** is not the address of an array. In your case the array is:

char files[num][maxLen+8];

so the function argument has to be a pointer to an array of maxLen+8:

int fillFileArr(char (* files)[maxLen+8], char * buf, int num) { 
etc...

Read this: http://bytes.com/forum/thread772412.html.

I'll check it out and look to it if I have the time - sort of in a hurry on this project, and this particular piece is not that critical...

Thanks for all the help - I'll look into this again when I have the time :)

[krreks]

Ok... I have made another atempt on the previously mentioned function - this time I hope it might work with some tweaking - different from the last code, which seemed impossible to implement :)

What I want to do is:
Take a pointer to a string and and some numbers giving the dimensions of the text (longest words and number of words) which is needed to allocate enogh memory for all the data. Then I will allocate memory, fill the pointers with data and return the char **.

char ** fillFileArr(char * buf, int num, int maxLen) {
	char ** arr = (char *) malloc(num);
	int y;

	for(y=0; y<num; y++) {
		arr[y] = (char *) malloc(maxLen+1);
	}
	
	int word=0, wordPos=0, bufferPos=0;
	while(word<num && buf[bufferPos]!='\0') {
		if(word==0 && wordPos==0 && bufferPos==0)
			printf("! ");
		if(buf[bufferPos]=='\n') {
			arr[word][wordPos] = '\0';
			
			if(buf[bufferPos+1]!='\0')
				printf("\n! ");
				      
			word++;
			wordPos=0;
		} else {
			arr[word][wordPos++] = buf[bufferPos];
			printf("%c", buf[bufferPos]);
		}
		bufferPos++;
	}
	
	return arr;
}

According to this article [http://stackoverflow.com/questions/4...arguments-in-c] (which my code is to a certain degree based upon) it should be possible to later on do a

arr[y][x];

on this data - right?

Yours sincerely

[arnaudk]

Check your types: is (char *) malloc(num) of type char** on line 2? Did you try to compile this code?

[krreks]

Check your types: is (char *) malloc(num) of type char** on line 2? Did you try to compile this code?

I tried both casting the malloc to (char **), (char *) and nothing - same result...

[donbock]

I tried both casting the malloc to (char **), (char *) and nothing - same result...

And what result was that?

By the way, I suggest you turn on all of the compiler warning options. Line 6 of post #6 should have provoked a compiler warning. You should resolve all compiler warnings before you try to execute your program.

[arnaudk]

I tried both casting the malloc to (char **), (char *) and nothing - same result...

But one of those is wrong. You'll probably save yourself some time if you read that article on arrays mentioned above. The correct form should be
char ** arr = (char **) malloc(num*(max Len+1)); now you have an array big enough to hold num strings of maxLen characters (plus '\0'), and drop the malloc() on line 6.

[krreks]

And what result was that?

By the way, I suggest you turn on all of the compiler warning options. Line 6 of post #6 should have provoked a compiler warning. You should resolve all compiler warnings before you try to execute your program.

It was late last night but as far as I remember i got seg faults in all three cases. I'm compiling with

gcc -o server server.c helpers.o protocol.o -I. -DDEBUG -g -Wall

[Banfa]

The correct form should be
char ** arr = (char **) malloc(num*(max Len+1));

Actually in C the correct form avoiding unrequired casts is

char ** arr = malloc(num*(max Len+1));

and in C++ the correct form is

char ** arr = new char *[num*(maxLen+1)];

assuming you want num*(maxLen+1) pointers although I would have thought that num pointers would be enough.

[arnaudk]

Actually in C the correct form avoiding unrequired casts is
char ** arr = malloc(num*(max Len+1));

Casting still silently takes place here since malloc always returns void*. Writing (char**) makes it more explicit but is indeed not required; some compilers may warn that implicit casting is taking place if on a 'paranoid' warning level, although probably not when casting from void, come to think of it.

assuming you want num*(maxLen+1) pointers although I would have thought that num pointers would be enough.

Right, assuming krreks wants to store num strings, each of length maxLen+1, then he'll need num pointers to char[maxLen+1] arrays;

char (*array)[num] = malloc(num*(maxLen+1)); // C
char (*array)[num] = new char[num][maxLen+1]; // C++

[Banfa]

Casting still silently takes place here since malloc always returns void*. Writing (char**) makes it more explicit but is indeed not required; some compilers may warn that implicit casting is taking place if on a 'paranoid' warning level.

True but I have see too many programmers silence implicit casting between types warnings with a cast when they had an actual error that needed fixing thus hiding the error.

The programmer should not put in casts by default, then if they get warnings they should be asking can I alter my code to remove with warning without a cast and only then if the answer is no should they put in a cast.

Explicit casting basically switches off all the compilers checks that things are being done correctly.

[arnaudk]

Ah, OK, I see your point.