Programming Forums > Application Development > C

trinath · Jan 14th, 2006, 10:47 AM

Hi all,

i have the following string as input :

"<iframe src="http://abcdef.com/asd/aaa/awerftya0480000008ave/direct;wi.120;hi.600/01?page=" frameborder="0" scrolling="no" marginheight="0" marginwidth="0" topmargin="0" leftmargin="0" allowtransparency="true" width="120" height="600">
<script language="JavaScript" type="text/javascript">
document.write('<a href="http://abcdefr.com/c/d/odmfndfdin000008ave/direct;wi.120;hi.600/01/" target="_blank"><img src="http://ssdfcreo.com/fed/up/asdasd58s5480000008ave/direct;wi.120;hi.600/01/"/></a>');
</script><noscript><a href="http://asedfr.com/bbb/cdf/sdfdf222200008ave/direct;wi.120;hi.600/01/" target="_blank"><img border="0" src="http://asd.com/asdas/ssd/asdeffee000008ave/direct;wi.120;hi.600/01/" /></a></noscript></iframe>"

also some more lenghty strings i need to write then into files.

for that i need to reaplce " to \" in this string .

please help me how can i replace so using a C program.

thanks in advance,

Trinath somanchi,
Hyderabad.

Ooble · Jan 14th, 2006, 10:51 AM

The easiest way would be to use a linked list (similar to C++'s std::string) for the text, and alter the node pointers whenever you find a ".

As an aside, IFrames and document.write(...) are generally not the best way to go about things when creating web sites.

trinath · Jan 14th, 2006, 11:02 AM

Can u be more clear

tempest · Jan 14th, 2006, 11:08 AM

trinath, first we aren't going to do the program for you.

Second, what are you talking about: how could this be used and what for? You have to start by trying to write the program, and then if you have a specific problem then we can help. This forum is for programmers not for those looking for programmers to do work for them.

trinath · Jan 14th, 2006, 11:46 AM

im clear at my side and written the program . but stuct at the posted point.how to replace " with \" is the problem

nindoja · Jan 14th, 2006, 1:18 PM

Here is what you can do:

Read through the input one character at a time and compare it to a double quote. If it is not a double quote write the character to a file that you have open. If it is a double quote, write \" to the file.

trinath · Jan 14th, 2006, 9:52 PM

This is really helpful for me
thank you nindoja

Ooble · Jan 15th, 2006, 7:35 AM

Writing to a file is not the best option if you're going to read the data straight back in again. To clarify on what I meant:

A linked list is the preferred method of getting around an array's limits - i.e. a fixed length. Using a linked list, you can increase and decrease the size as necessary. This will be a very quick run-through - for a more detailed explanation, check your book on C. It will most likely have lots of diagrams to help you understand the process.

Linked lists use pointers to function. If you don't know how they work, I suggest you check them out - they're pretty fundamental to C. Linked lists are simply a series of nodes connected together:

(Toggle Plain Text)

struct Node
{
	char data;
	Node* next;
}

This structure contains two pieces of data: a character, where you can store a single byte of data, and a pointer to the next node. By linking these together, you can create a string:

(Toggle Plain Text)

	const char my_string[] = "This is a string.";
	Node* start = NULL;
	Node* current = start;
	int index;
	
	for (index = 0; my_string[index]; index++) /* loops through my_string */
	{
		/* if current is not a null pointer, we create another Node and point to that instead */
		if (current)
		{
			current->next = malloc(sizeof(Node));
			current = current->next; /* moves us onto the next Node */
		}
		
		/* copy the data into the current Node */
		current->data = my_string[index];
		current->next = NULL;
	}

This code copies the string in my_string to a linked list pointed at by start. To print the data in the linked list, we just loop through it:

(Toggle Plain Text)

int print (Node* start)
{
	Node* current = start;
	int length = 0;
	
	/* we do this until current is a null pointer */
	while (current)
	{
		printf("%c", current->data);
		length++;
		
		current = current->next;
	}
	
	return length;
}

But what benefit does this linked list have over a standard array of characters? With everything we've seen, they seem to be more complicated. Well, let's find out.

Because of the list's pointer-based nature, it isn't limited to a specific length and order. In fact, we can now add and remove characters anywhere in the string without having to duplicate it. Let's take a look at an insertion function:

(Toggle Plain Text)

int insert (Node* start, char character, int position)
{
	Node* current = start;
	int i;
	
	/* gets us to the position we want */
	for (i = 0; i < position; i++)
	{
		if (current->next)
		{
			current = current->next;
		}
		else
		{
			/* if the string isn't that long, we return -1 as an error code */
			return -1;
		}
	}
	
	/* inserts the character */
	Node* new_node = malloc(sizeof(Node)); /* creates a new node for the character to be held in */
	new_node->data = character;
	
	/* the following two statements insert it in between current and current->next, or position and position + 1
	 * this works even if current->next == NULL */
	new_node->next = current->next;
	current->next = new_node;
	
	return i;
}

You can use this insertion function to insert the backslashes wherever you want. I'll leave it to you to work out the rest.

Enjoy. If there are any questions (and I expect some - this isn't exactly the easiest tutorial to follow), don't hesitate to ask.

As an aside, there is a class in C++ called std::string which nicely encapsulates this concept in an easy-to-use datatype. You might find it easier just to switch to C++.

Polyphemus_ · Jan 15th, 2006, 7:38 AM

The only problem with using a linked list is that one character takes 5 bytes in total.

Ooble · Jan 15th, 2006, 7:39 AM

Much easier than insertion by duplication though, isn't it?

Jan 14th, 2006, 10:47 AM	#1
trinath Newbie Join Date: Jan 2006 Posts: 4 Rep Power: 0	String Manipulation in C Hi all, i have the following string as input : "<iframe src="http://abcdef.com/asd/aaa/awerftya0480000008ave/direct;wi.120;hi.600/01?page=" frameborder="0" scrolling="no" marginheight="0" marginwidth="0" topmargin="0" leftmargin="0" allowtransparency="true" width="120" height="600"> <script language="JavaScript" type="text/javascript"> document.write('<a href="http://abcdefr.com/c/d/odmfndfdin000008ave/direct;wi.120;hi.600/01/" target="_blank"><img src="http://ssdfcreo.com/fed/up/asdasd58s5480000008ave/direct;wi.120;hi.600/01/"/></a>'); </script><noscript><a href="http://asedfr.com/bbb/cdf/sdfdf222200008ave/direct;wi.120;hi.600/01/" target="_blank"><img border="0" src="http://asd.com/asdas/ssd/asdeffee000008ave/direct;wi.120;hi.600/01/" /></a></noscript></iframe>" also some more lenghty strings i need to write then into files. for that i need to reaplce " to \" in this string . please help me how can i replace so using a C program. thanks in advance, Trinath somanchi, Hyderabad.

Jan 14th, 2006, 10:51 AM	#2
Ooble I eat cake for breakfast. Join Date: Jul 2004 Location: In my box. Posts: 4,434 Rep Power: 9	The easiest way would be to use a linked list (similar to C++'s std::string) for the text, and alter the node pointers whenever you find a ". As an aside, IFrames and document.write(...) are generally not the best way to go about things when creating web sites. __________________ Me :: You :: Them

Jan 14th, 2006, 11:08 AM	#4
tempest Programming Guru Join Date: Oct 2004 Posts: 1,041 Rep Power: 5	trinath, first we aren't going to do the program for you. Second, what are you talking about: how could this be used and what for? You have to start by trying to write the program, and then if you have a specific problem then we can help. This forum is for programmers not for those looking for programmers to do work for them. __________________

Jan 15th, 2006, 7:35 AM	#8
Ooble I eat cake for breakfast. Join Date: Jul 2004 Location: In my box. Posts: 4,434 Rep Power: 9	Writing to a file is not the best option if you're going to read the data straight back in again. To clarify on what I meant: A linked list is the preferred method of getting around an array's limits - i.e. a fixed length. Using a linked list, you can increase and decrease the size as necessary. This will be a very quick run-through - for a more detailed explanation, check your book on C. It will most likely have lots of diagrams to help you understand the process. Linked lists use pointers to function. If you don't know how they work, I suggest you check them out - they're pretty fundamental to C. Linked lists are simply a series of nodes connected together: (Toggle Plain Text) struct Node { char data; Node* next; } struct Node { char data; Node* next; } This structure contains two pieces of data: a character, where you can store a single byte of data, and a pointer to the next node. By linking these together, you can create a string: (Toggle Plain Text) const char my_string[] = "This is a string."; Node* start = NULL; Node* current = start; int index; for (index = 0; my_string[index]; index++) /* loops through my_string / { / if current is not a null pointer, we create another Node and point to that instead / if (current) { current->next = malloc(sizeof(Node)); current = current->next; / moves us onto the next Node / } / copy the data into the current Node / current->data = my_string[index]; current->next = NULL; } const char my_string[] = "This is a string."; Node start = NULL; Node* current = start; int index; for (index = 0; my_string[index]; index++) /* loops through my_string / { / if current is not a null pointer, we create another Node and point to that instead / if (current) { current->next = malloc(sizeof(Node)); current = current->next; / moves us onto the next Node / } / copy the data into the current Node / current->data = my_string[index]; current->next = NULL; } This code copies the string in my_string* to a linked list pointed at by start. To print the data in the linked list, we just loop through it: (Toggle Plain Text) int print (Node* start) { Node* current = start; int length = 0; /* we do this until current is a null pointer / while (current) { printf("%c", current->data); length++; current = current->next; } return length; } int print (Node start) { Node* current = start; int length = 0; /* we do this until current is a null pointer / while (current) { printf("%c", current->data); length++; current = current->next; } return length; } But what benefit does this linked list have over a standard array of characters? With everything we've seen, they seem to be more complicated. Well, let's find out. Because of the list's pointer-based nature, it isn't limited to a specific length and order. In fact, we can now add and remove characters anywhere in the string without having to duplicate it. Let's take a look at an insertion function: (Toggle Plain Text) int insert (Node start, char character, int position) { Node* current = start; int i; /* gets us to the position we want / for (i = 0; i < position; i++) { if (current->next) { current = current->next; } else { / if the string isn't that long, we return -1 as an error code / return -1; } } / inserts the character / Node new_node = malloc(sizeof(Node)); /* creates a new node for the character to be held in / new_node->data = character; / the following two statements insert it in between current and current->next, or position and position + 1 * this works even if current->next == NULL / new_node->next = current->next; current->next = new_node; return i; } int insert (Node start, char character, int position) { Node* current = start; int i; /* gets us to the position we want / for (i = 0; i < position; i++) { if (current->next) { current = current->next; } else { / if the string isn't that long, we return -1 as an error code / return -1; } } / inserts the character / Node new_node = malloc(sizeof(Node)); /* creates a new node for the character to be held in / new_node->data = character; / the following two statements insert it in between current and current->next, or position and position + 1 * this works even if current->next == NULL */ new_node->next = current->next; current->next = new_node; return i; } You can use this insertion function to insert the backslashes wherever you want. I'll leave it to you to work out the rest. Enjoy. If there are any questions (and I expect some - this isn't exactly the easiest tutorial to follow), don't hesitate to ask. As an aside, there is a class in C++ called std::string which nicely encapsulates this concept in an easy-to-use datatype. You might find it easier just to switch to C++. __________________ Me :: You :: Them

Jan 15th, 2006, 7:39 AM	#10
Ooble I eat cake for breakfast. Join Date: Jul 2004 Location: In my box. Posts: 4,434 Rep Power: 9	Much easier than insertion by duplication though, isn't it? __________________ Me :: You :: Them

Jan 14th, 2006, 11:02 AM	#3
trinath Newbie Join Date: Jan 2006 Posts: 4 Rep Power: 0	Can u be more clear

Jan 14th, 2006, 11:46 AM	#5
trinath Newbie Join Date: Jan 2006 Posts: 4 Rep Power: 0	im clear at my side and written the program . but stuct at the posted point.how to replace " with \" is the problem

Jan 14th, 2006, 1:18 PM	#6
nindoja Programmer Join Date: Jun 2005 Posts: 92 Rep Power: 4	Here is what you can do: Read through the input one character at a time and compare it to a double quote. If it is not a double quote write the character to a file that you have open. If it is a double quote, write \" to the file.

Jan 14th, 2006, 9:52 PM	#7
trinath Newbie Join Date: Jan 2006 Posts: 4 Rep Power: 0	This is really helpful for me thank you nindoja

Jan 15th, 2006, 7:38 AM	#9
Polyphemus_ Expert Programmer Join Date: Aug 2005 Location: Rotterdam, the Netherlands Posts: 942 Rep Power: 4	The only problem with using a linked list is that one character takes 5 bytes in total.

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Programming Forums > Application Development > C

String Manipulation in C