Checking words in a string.

Hi,

So an exercise I have is to read each line from a input file to determine if an arbitrary words is used in each of the lines. I have read the file in and used getline to store each line in a string. However, Im not sure how to then loop through the string to see if the word is there? Do I have to break the string down and store in a vector? The code so far is:

Code:

cout << "Enter file name: ";
	string name;
	cin >> name;

	ifstream ist(name.c_str());

	cout << "Enter a word to search for: ";
	string word;
	cin >> word;

	
	string s;

	while(!ist.eof()){
		getline(ist,s);
		
		
		
	}

Thanks.

I think i've found it now. Should I be using the find member function. Such as s.find(word)?

Thanks.

Originally Posted by darren78

I think i've found it now. Should I be using the find member function. Such as s.find(word)?

Thanks.

Nope, thats not working. Any suggestions?

Thanks.

find should work. Also note that you should always use getline. Do not mix cin >> and getline. It will only bring trouble.
I suggest you post your attempt with find if you can't get it to work.

Originally Posted by Elysia

find should work. Also note that you should always use getline. Do not mix cin >> and getline. It will only bring trouble.
I suggest you post your attempt with find if you can't get it to work.

So when needing input from just the console, should I also use getline?

The code for find is as follows

Code:

string s;
	int counter = 0;

	while(!ist.eof()){
		getline(ist,s);

		if(s.find(word))
			cout << word << " has been found on line " << counter
			<< ": " << s << endl;

		++counter;	
		
	}

The output is not what I am expecting. There are 3 lines in the file, with the word I am looking for only on the first line. Instead it disregards my first line completely, then says that it has been found on lines 2 and 3 and then prints two blank "has been found on line"?

Any suggestions?

Thanks again.

I suggest you look up the function find in your local C++ reference.

Originally Posted by Elysia

I suggest you look up the function find in your local C++ reference.

I've done as you suggested and it now works.

Code:

string::size_type index = s.find(word);
		if(index != string::npos)
			cout << s.substr (index) << endl;

Thanks.

No problem.

Originally Posted by darren78

So when needing input from just the console, should I also use getline?

cin.getline -- used with c-style character arrays
getline(cin ...) used with c++ std::string.
cin -- used with int's, double's, chars,etc. Security Issue (Allows for buffer over-run - no delimiter checking).

If possible, use cin.getline(VAR, DELIMITER) where 'var' is where to store the input, and DELIMITER is where/when to stop - such as '\n' or 10.

[s]I wish I could provide a resolution to the other issues[/s] Good job Elysia

I've never found any real good use for cin >>. Now, string streams >> operator can be rather handy at times, however, when extracting data from a string.
If possible, use std::getline to avoid C-style strings. It also supports the delimiter.

Originally Posted by darren78

I've done as you suggested and it now works.

Code:

string::size_type index = s.find(word);
		if(index != string::npos)
			cout << s.substr (index) << endl;

Thanks.

Can I just check with you that I fully understand what this is doing. Am I correct in thinking that the size_type index, will (if the word is there) store where the word starts and if its not found it has the value end of string?
Then by checking that the index isnt equal to end of string (npos), it prints out the line? I dont understand what s.substr(index) does though. I mean, I know that its printing the line, but how?

Thanks.

Yes, find returns the index where the string you're looking for begins, and if not found, it returns std::string::npos. So you check against this to see if it found it or not.
std::string::substr is a function that returns a substring, ie a part of another string. It takes two arguments, the first of which indicates the start position of the substring. Since you are specifying the second parameter, it takes everything in the string from the index position and returns it.

For example:

Code:

std::string str("Hello World!");
auto index = str.find("World!"); // C++0x feature
std::cout << str.substr(index); // Prints out "World!".

Thanks, thats crystal clear now. And thanks CC for your help too.

I'm going to be starting a 12 month placement in 8 weeks so doing some intensive cramming now ready for it. So I may be on quite a bit over the next couple of weeks

Originally Posted by darren78

Thanks, thats crystal clear now. And thanks CC for your help too.

I'm going to be starting a 12 month placement in 8 weeks so doing some intensive cramming now ready for it. So I may be on quite a bit over the next couple of weeks

Check up on the C++ book recommendations (I suggest C++ Without fear && || Sams Teach Yourself C++ in an hour a day). First work on general or procedural based programming, then move towards structured programming and then of course object oriented programming (OOP).

Incase your wondering:

-Procedural programming: The code is listed 'as is' in the fashion that it will be run. This code is listed from a-z (a will be run first, z will be run last).

-Structured programming: Splitting apart your code into more manageable piece of code, usually by taking chunks of procedure based code and putting it into reasonable functions.

-Object orientated programming: An 'object' way of performing tasks. You may go from a to c, to f to z, then back to a. In OOP you enforce the rule of usability and DRY methods. Dry stands for 'do not repeat yourself'.

I've turned this into a lecture :P

I suggest Accelerated C++ because it simply teaches C++ first and the C parts of C++ later. Simply put, it is the best novice book I know.