Thread: String issues

Hey,

I am writing a palindrome app for a class. I'm having a problem though using size() or length() for the string lengths. I keep getting a typecast error but I am almost sure I am writing it correctly (I have searched the boards, read the FAQ, and looked in my book). I see multiple examples written this way:

Code:

#include <iostream>
#include <string>
#include <cctype>

using namespace std;

int main() {
	string s;
	int x;

	cout << "Enter a string:" << endl;
	cin >> s;
	x = s.size();
	cout << endl << "The string " << s << " is " << x << " characters long." << endl;
	return 0;
}

On compile I get the following error:

Code:

c:\Documents and Settings\Josh\My Documents\Visual Studio Projects\strings\strings\strings.cpp(13) : warning C4267: '=' : conversion from 'size_t' to 'int', possible loss of data

Im using Visual Studio 7.0. I know it's just a warning but is there anyway to make it right?

Thanks,
Joshua Norton

Just change your declaration to:

size_t x;

I also get
"signed unsigned mismatch" when comparing the size to an int in a for loop.

Not sure what a size_t is. Im guessing it's a type created in the string header or something? Is it just like an int or what?

Thanks,
Joshua Norton

Certainly fixed all the errors though. I will search for it and try and find info. Thanks for the help Sebastiani.

~Joshua Norton

Originally posted by Josh Norton
I also get
"signed unsigned mismatch" when comparing the size to an int in a for loop.

Not sure what a size_t is. Im guessing it's a type created in the string header or something? Is it just like an int or what?

Thanks,
Joshua Norton

Its defined in stddef.h and few other files. Its defined as

Code:

typedef unsigned int size_t;

>typedef unsigned int size_t;
Not necessarily. The standard only specifies that size_t is an unsigned integer type of the result of the sizeof operator. That doesn't mean that it actually is unsigned int. If it were then we wouldn't need a typedef, would we?

I know comparing a syze_t type to an int in my for loop caused a seg fault. I guess since size_t was unsigned and being compared to a negative value(or so I assumed)? I changed "i" to an int and it was fine. I can't get rid of the warning though. I'm guessing you could cast it somehow and make it right?

~Joshua Norton

>I guess since size_t was unsigned and being compared to a negative value
That would be a good guess.

>I can't get rid of the warning though.
Post the loop in question, the declarations of variables involved, and the warning you get.

I'll just post it all... It's not an error. Just a warning. It reads:

Code:

lab7.cpp(93) : warning C4267: 'initializing' : conversion from 'size_t' to 'int', possible loss of data

The loop I had the comparison in is near the bottom. In the palindromEval() function. I commented a note above it.

Code:

//name:  Lab 7
//author:  Joshua Norton
//description:  This program is designed to take in a string from the user(punctuation and whitespace are BOTH accepted)
//				and determine if that string is a palindrome or not.

#include <iostream>
//cctype is included for the ifpunct() and ifspace() functions
#include <cctype>
#include <string>

using namespace std;

string stringStrip(string userString);
bool palindromeEval(string originalString);

int main(void) {
	int quit = 0;
	bool mismatch = false;
	string userString, originalString;

	//menu loop
	while(quit != 2) {
		quit = 0;
		//menu options
		cout << "Please choose from the following options:" << endl << endl
		     << "1) Evaluate a new string to see if it's a plaindrome." << endl
		     << "2) Quit." << endl << endl;
	 
		cin >> quit;

		switch(quit) {
			case 1:
				//prompt the user for a string
				cout << "Please enter the string you would like to evaluate." << endl;
				//I had some trouble with the getline function.  I guess VS7 leaves a return character in the input buffer
				//which causes the getline function to exit without ever prompting the user for input.  I found quite a few
				//posts regarding the subject and the concensous for handling it seemed to be the cin.ignore command
				cin.ignore();
				//intake the users string
				getline(cin, userString);
				originalString = stringStrip(userString);

				if(palindromeEval(originalString)) {
					//mismatch true
					cout << endl << endl << "------------------------------------------------" << endl
					     << "Sorry, \"" << userString << "\" is not a palindrome." << endl
						 << "------------------------------------------------" << endl << endl;
				} else {
					//mismatch false
					cout << endl << endl << "------------------------------------------------" << endl
						 << "\"" <<  userString << "\" is a palindrome!" << endl
						 << "------------------------------------------------" << endl << endl;
				}
				break;
			case 2:
				cout << "Quitting..." << endl;
				break;
			//validation for the menu
			default:
			cout << "You have entered an invalid option." << endl << endl;
			break;
		}
	}
	return 0;
}
//the stringStrip() function removes puncuation and whitespace from the original string then sets it all lowercase.
string stringStrip(string userString) {
	string originalString;
	size_t i, len;
	len = userString.size();

	//copy only chars that are not whitespace or punctuation
	for(i = 0; i < len; i++) {
		if((!isspace(userString[i])) && (!ispunct(userString[i]))) {
			originalString += userString[i];
		}
	}
	//set string to lowercase
	for(i = 0; i < originalString.size(); i++) {
		originalString[i] = tolower(originalString[i]);
	}
	return originalString;
}

//palindromeEval creates a reverse copy of the formatted string and compares the 2 strings to see if they are a palindrome
bool palindromeEval(string originalString) {
	bool mismatch = false;
	string reverseString;
	size_t len = originalString.size();

                 //This loop right here used to read for(size_t i = len-1...
	//create a reverse copy of the string
	for(int i = len-1; i >= 0; i--) {
		reverseString += originalString[i];
	}

	//compare the strings to see if they are a palindrome
	if(originalString == reverseString) {
		mismatch = false;
	} else {
		mismatch = true;
	}
	
	return mismatch;
}

You should avoid mixing signed and unsigned variables. It causes more problems than you can imagine. You can modify your loop so that using unsigned quantities will work correctly, or you can make len an int and silence the warning there by casting originalString.size() to int as well.

I've just compiled and ran your code through MSVC++ 6.0 and Dev C++.. I didn't get a single warning or error so I guess your problem maybe with your compiler...
But I'm guessing as prelude said

Not necessarily. The standard only specifies that size_t is an unsigned integer type of the result of the sizeof operator. That doesn't mean that it actually is unsigned int.

Seeing as len doesn't really have a type it is warning you that comparing the unsigned integer from possibly two different types could result in information loss (e.g. think what happens when you round off a float number you loose some info.) you want to get rid of it.. the make len an usigned int. It's a warning that can be ignored in this case me thinks but others will disagree.

ok. When I had 'i' declared size_t and the loop got below zero it was seg faulting since i would roll over(I guess) to the max value for an unsigned int( 4294967295 when I just tried it). I'm not sure how I would format the for statement to get the [0] element of the string without 'i' being decremented past 0. Maybe if I inserted a dummy character into the string at [0] and then accounted for it. Probably easier just to cast 'len' though.

>I'm not sure how I would format the for statement to get the [0] element of the string without 'i' being decremented past 0.
The most obvious way would be an unsigned-safe loop followed by a redundant body handling index 0. This avoids a cast and allows you to more obviously handle edge cases:

Code:

string::size_type len = originalString.size();

if (len > 1) {
  // For strings with 2 or more characters
  for(string::size_type i = len; i > 1; ) {
    reverseString += originalString[--i];
  }
  reverseString += originalString[0];

  if(originalString == reverseString) {
    mismatch = false;
  } else {
    mismatch = true;
  }
} else {
  // Strings with 1 or 0 characters are always a palindrome
  mismatch = false;
}