Thread: Pointers & char arrays

I'm triying to make a function to get something from the middle of another 2 strings, this is what I've got..
The code goes trough the string using it's lenght in a for loop, while it goes trough, it starts finding the letters from the first item and also increments j, to look for the other letter and if it is not found, it resets it, then if j is equal to the first item's lenght, it continues with the second one and it does the same, but if it is equal to the second item lenght it returns the string in between

Code:

char *getFromMiddle(char *string, int l_string, char *first, int l_first, char *second, int l_second) { // the function has to return a char pointer, is it well declared?
	int i, j, x, f_pos, s_pos, l_middle;
	char t, *middle;
	printf("Declara variables \n");
		for(i=0;i<l_string;i++) {
			printf("For numero: %i \n", i);
			if(x != 1) {
				if(*string[i] == *first[j]) { //trouble here
					printf("Igualdad entre i nº=%i(%c) con j nº=%i(%c): %i \n", i, string[i], j, first[j]);
					j++;
					if(j == l_first) {
					printf("J(%i) = l_first(%i)",j ,i);
						f_pos = i;
						j = 0;
						x = 1;
					}
				}
				else {
					printf("No se encontro igualdad en i->%i(%c) == j->%i(%c)",i ,string[i], j, first[j]);
					j = 0;
				}
			}
			else {
				if(*string[i] == *second[j]) { // also here
					j++;
					if(j == l_second) {
						s_pos = i-l_second;
						l_middle = s_pos-f_pos;
						middle = malloc(sizeof(t)*(l_middle+1));
						for(x=0;x<l_middle;x++) {
							*middle[x] == *string[f_pos];
							f_pos++;
						}
						*middle[l_middle+1] = '\0';
						return middle; // is it middle well returned?
					}
				}
				else {
					j = 0;
				}
			}
		}
	return 0; // return 0 if nothing was found
}

I'm having troubles with the pointers and the char arrays, how can I use them as a classic char array? Also I don't really know if the return variable will be a char pointer..
Thanks

Originally Posted by lautarox

I'm having troubles with the pointers and the char arrays, how can I use them as a classic char array? Also I don't really know if the return variable will be a char pointer..
Thanks

What do you mean by "classic char array"? And why are you dereferencing everywhere:

Code:

if(*string[i] == *first[j]) { //trouble here

English is not your first language so I will let you know: this sentence makes no sense, so it's hard to decide what your intent is:

I'm triying to make a function to get something from the middle of another 2 strings

You never set j (or x) to 0, either, meaning they could be anything from the start. I would say this code obviously does not work at all, and you are making a big mistake writing so much without *any* of it working. It is a *very bad idea* to just write a huge block like this presuming it will all work before you try and compile even once. You should break the task down into smaller steps so that you can write something simple, make sure it works the way you intend, and then get more complicated.

English is not your first language so I will let you know: this sentence makes no sense, so it's hard to decide what your intent is:

You are right =P
I'm triying to make a function, to get a string from the middle of two items, like <hello>asas</hello>, the function should get asas.
I mean like a "classic" -> normal char array, is it possible to use the pointer with the [] tags as the char array?
By the way, thanks for your time

Yep! it is possible to use [] as an alternative to the pointer "->" notation

How could it be used? an example will be appreciated.
I'll try using strtok()
Edit*, I won't be able to use strtok(), because of the large ammount of tags in the string..

Originally Posted by lautarox

How could it be used? an example will be appreciated.
I'll try using strtok()

Here's a short example that might help if you also read some documentation:

Code:

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

int main() {
	char string[]="<h1>Example</h1>",*tok;
	tok=strtok(string,"<>");
	printf("%s\n",tok);
	while ((tok=strtok(NULL,"<>"))) printf("%s\n",tok);
        printf("Now string=%s\n",string);
	return 0;	
}

Notice that the *first* strtok() uses "string", and after that NULL since this is already set. Also be aware that this does strange things to "string" itself, which is shown with the last printf.

That may or may not be useful to you, depending on the context. Your original idea is not a bad one, you just need to work it out more slowly and always try and keep it so that you can compile and test (with printf for debugging) every couple of lines -- even if this means making small simplifications that are not permanent.

Thanks MK27, but I think that strtok() won't work because of the large amount of tags the string has, could you tell me how could I access the value of a character from the pointer string using the [] tags? that's what I need to continue debugging the code.
Example:
// ptr is a pointer, and so it is ptr2
I want it to point to the (1) character, it would be the second counting from the 0, so it would compare the value they have.
if(ptr[1] == ptr2[1]) { ...

Originally Posted by lautarox

Thanks MK27, but I think that strtok() won't work because of the large amount of tags the string has, could you tell me how could I access the value of a character from the pointer string using the [] tags? that's what I need to continue debugging the code

strtok() will work on a longer string too, but here's something that demonstrates the proper syntax for passing a C string and accessing it's individual elements (characters):

Code:

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

void tagsout (char *ptr) {
	int len = strlen(ptr), i, j=0, tag=0; /* "tag" is a flag */
	char tmp[len];
	for (i=0; i<len; i++) {
		if (ptr[i]=='<') tag=1;
		if (ptr[i]=='>') { tag=0; continue; }
		if (tag) continue;  /* flag is set, so skip */
		tmp[j]=ptr[i]; j++;  /* or add to tmp and advance j counter */
	}
	tmp[j]='\0'; /* null terminate replacement */
	strcpy(ptr,tmp);
}
		

int main() {
	char string[]="<div class=\"this\"><p>Hello</p><center><h1>Example</h1></center></div>";
	tagsout(string);
	printf("%s\n",string);
	return 0;	
}

Hopefully that will at least get you started...