Find Text error i think

Using Arduino Programming Questions
1

Not sure if I'm reporting this in the correct location.

I am quite sure I have discovered an error in the example code found on the following link.

Find Text Example code on this site:
http://playground.arduino.cc/Main/FindText

char Haystack[] = "this is a test";
char Needle[] = "test";
Serial.println(find_text(Needle, Haystack));

returns -1

Clearly "test" is located in the string

for (int i = 0; (i < haystack.length() - needle.length()); i++) {
should read:
for (int i = 0; (i <= haystack.length() - needle.length()); i++) {

now it returns 10

Hope this helps someone :slight_smile:

2

Thank you. I have changed it. That code is for String objects. For normal text the strstr() could be used.

3

Thank you
I forgot about strstr()

glad I could help :slight_smile:

4

to use strstr() in the same way as find_text() i had to do the following

 char Haystack[] = "this is a test";
  char Needle[] = "test";
  Serial.println(Haystack);
  Serial.println(Needle);
  char * Pointer;
  Pointer = strstr(Haystack, Needle);
  Serial.println(&Pointer[0] - &Haystack[0]); // subtract the starting pointer of Haystack from the pointer returned by strstr()
  Serial.println(find_text(Needle, Haystack));

Returns 10 for both tests :slight_smile:

again thank you for the strstr()

5

Hi guys! I know this post is a bit old, but since it helped me a lot when looking for a simple, clean way to find text in strings, I decided to put my 2 cents in.
In case the needle is bigger than the haystack, the for loop will never end, which is not what a for loop is meant for in the first place, so it must be placed in a conditional if() or while() (I like to code with those two mostly). For example, it would look like this:

int find_text(String needle, String haystack)
{
int foundpos = -1;
if (needle.length() <= haystack.length())
{
for (int i = 0; i <= haystack.length() - needle.length(); i++)
{
if (haystack.substring(i,needle.length()+i) == needle)
foundpos = i;
}
}
return foundpos;
}

EDIT: I decided to post this so this "bug" would be considered and put in the description of the Arduino Playground site. Or use my code. Either way, I think it must be considered and mentioned for posterity.

6

In case the needle is bigger than the haystack, the for loop will never end

If needle.length() is 20 and haystack.length() is 10, the for loop will be

   for (int i = 0; i <= -10; i++)

That reads "starting with i equal to 0, while i is less than or equal -10, do some stuff, increment i by 1, and check the while condition again.

Since 0 is not less than, or equal to -10, the body of the for statement will never be executed.

The if test you added is not needed. The "bug" is in your understanding of a for statement.