Back to General and Gameplay Programming

strcmp

General and Gameplay Programming Programming

Started by discodowney October 12, 2011 02:28 PM

4 comments, last by Concentrate 12 years, 6 months ago

discodowney

102

Author

October 12, 2011 02:28 PM

So i have an expression. Its just a simple bracketed addition sum. (4 + 2). The important parts of the code are below.







char *exp = "(4 + 2)";

int result = 0;



evaluate(exp, result);





bool evaluate(const char *expression, int &result)

{

	while(expression)

	{   		

 			if (!checkIfValid(expression))

     			return false;



     		if(strcmp(&expression, "(")==0)

 			{

                  blah;

                  blah;

                  blah;

 			}



      i++;



	}

}



bool checkIfValid(const char expression)

{

	if(isdigit(expression) || strcmp(&expression, "(")==0 || strcmp(&expression, ")")==0 ||

		strcmp(&expression, "+")==0  || strcmp(&expression, "/")==0 || strcmp(&expression, "*")==0 ||

		strcmp(&expression, "-")==0 || isspace(expression))	

		return true;

	else 

		return false;

}

the problem I'm having is that the checkIfValid method will return true when a bracket is put in. Thats fine, thats supposed to happen. But when i use the same code, if(strcmp(&expression, "(")==0), in the next if it fails. Can anyone see why this is? The only difference is the use of subscripting to say which char in the expression im comparing, but subscripting shouldnt be a problem should it?

Cheers

BradBobak_68669

137

October 12, 2011 02:35 PM

strcmp() requires a '\0' terminated string. Since you are passing a char by value to checkIfValid, sending the address of this char to strcmp(), it will probably not find a '\0' right after the char in memory. Since you are comparing only to one character, why not just if (expression == '(' || expression == ')'), etc.

Edit:

Also, your strcmp(&expression, "(") isn't satisfied because strcmp is checking all chars from (expression + i) to the end of the string (the '\0'). again, since you are only checking one character, if (expression == '(') should suffice.

discodowney

102

Author

October 12, 2011 02:40 PM

Sound man, Thanks. I've not used strcmp much at all, so wasnt sure how to go about this.

ApochPiQ

23,138

October 12, 2011 06:23 PM

Since you appear to be using C++, the correct thing to do is use std::string for handling anything longer than a single char.

Wielder of the Sacred Wands
[Work - ArenaNet] [Epoch Language] [Scribblings]

the_edd

2,109

October 12, 2011 06:32 PM

bool checkIfValid(const char expression) { if(isdigit(expression) || strcmp(&expression, "(")==0 || strcmp(&expression, ")")==0 || strcmp(&expression, "+")==0 || strcmp(&expression, "/")==0 || strcmp(&expression, "*")==0 || strcmp(&expression, "-")==0 || isspace(expression)) return true; else return false; }

If you're only wanting to compare a single char, as appears to be the case in all these strcmp() calls, just use the built-in equality operator for char:



bool checkIfValid(char ch)

{

	return isdigit(ch) || isspace(ch) || ch == '(' || ch== ')' || ch == '+' || ch == '/' || ch == '*' || ch == '-';

}

Or:



bool checkIfValid(char ch)

{

	return isdigit(ch) || isspace(ch) || (ch != '\0' && strchr("()+/*-", ch));

}

Though I also tend to agree with ApochPiQ's comment about std::string usage.

http://www.mr-edd.co.uk
http://bitbucket.org/edd

Concentrate

181

October 14, 2011 05:09 AM

Maye...



bool isValid(char ch){

 const std::string validChars = "()+/*-";

 return isdigit(ch) || isspace(ch) || validChar.find(ch) != string::npos;

Edge cases will show your design flaws in your code!
Visit my site
Visit my FaceBook
Visit my github

strcmp

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

strcmp

This topic is closed to new replies.

Popular Topics

Recommended Tutorials

Reticulating splines