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Segmentation Fault

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Join Date: Jun 2009

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TrintiyNoe TrintiyNoe is offline

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Segmentation Fault

Jul 5th, 2009

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include<iostream>
#include<vector>
#include<sstream>
#include<algorithm>
#include<cmath>
#include<string>
using namespace std;
 
class ComboLength
{
	public:
	int howLong(string moves)
	{
		vector<int> cc;
		int i,j,k=0;
		for(i=0;i<moves.size()-1;++i)
		{
			if(moves[i]==moves[i+1])       //Error
			k++;
			else
			cc.push_back(k);
		}
		return *max_element(cc.begin(),cc.end());
	}
};
#include<iostream>
#include<vector>
#include<sstream>
#include<algorithm>
#include<cmath>
#include<string>
using namespace std;

class ComboLength
{
	public:
	int howLong(string moves)
	{
		vector<int> cc;
		int i,j,k=0;
		for(i=0;i<moves.size()-1;++i)
		{
			if(moves[i]==moves[i+1])       //Error
			k++;
			else
			cc.push_back(k);
		}
		return *max_element(cc.begin(),cc.end());
	}
};

I get a segementaion error in line if (moves[i]==moves[i+1])
any idea why?

Last edited by TrintiyNoe; Jul 5th, 2009 at 3:31 am. Reason: Added code tages

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Join Date: Jan 2009

Posts: 476

Reputation: csurfer is just really nice

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csurfer

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Re: Segmentation Fault

Jul 5th, 2009

Why calling the function moves.size() again and again for every loop ??? Do it once,else its just a waste of computation time.

Do this :

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 c++ Syntax (Toggle Plain Text) 
int max=moves.size()-1;
for(i=0;i<max;++i)
{
	if(moves[i]==moves[i+1])       
		k++;
	else
		cc.push_back(k);
}
int max=moves.size()-1;
for(i=0;i<max;++i)
{
	if(moves[i]==moves[i+1])       
		k++;
	else
		cc.push_back(k);
}

And with respect to the segmentation fault I am not finding any problem with the code.Well may be its not because of the statement you said.

Last edited by csurfer; Jul 5th, 2009 at 4:06 am.

I Surf in "C"....

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Laiq Ahmed Laiq Ahmed is offline

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Re: Segmentation Fault

Jul 5th, 2009

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Originally Posted by TrintiyNoe

Help with Code Tags

C++ Syntax (Toggle Plain Text)
#include<iostream>
#include<vector>
#include<sstream>
#include<algorithm>
#include<cmath>
#include<string>
using namespace std;
 
class ComboLength
{
	public:
	int howLong(string moves)
	{
		vector<int> cc;
		int i,j,k=0;
		for(i=0;i<moves.size()-1;++i)
		{
			if(moves[i]==moves[i+1])       //Error
			k++;
			else
			cc.push_back(k);
		}
		return *max_element(cc.begin(),cc.end());
	}
};
#include<iostream> #include<vector> #include<sstream> #include<algorithm> #include<cmath> #include<string> using namespace std; class ComboLength { public: int howLong(string moves) { vector<int> cc; int i,j,k=0; for(i=0;i<moves.size()-1;++i) { if(moves[i]==moves[i+1]) //Error k++; else cc.push_back(k); } return *max_element(cc.begin(),cc.end()); } };
I get a segementaion error in line if (moves[i]==moves[i+1])
any idea why?

i can see the problem here..

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 C++ Syntax (Toggle Plain Text) 
return *max_element(cc.begin(),cc.end());
return *max_element(cc.begin(),cc.end());

it shouldn't be like that, what if no values are being inserted in the vector. and your test [icode] moves[i] == moves[i+1] succeeded all the time then vector "cc" will be empty and max_elements return the last iterator which is not an element. and dereferencing an unknown element is segmentation fault.. (in complete description but sufficient at this level).

so change this code to following.

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 C++ Syntax (Toggle Plain Text) 
    vector<int>::iterator maxIter = max_element(cc.begin(),cc.end());
    if (maxIter != cc.end()){ 
         return *maxIter;               // not a good way either. but will work.
    } 
    else {
         return -1;                       // logically indicatting no value depends on implementation.
    }
    vector<int>::iterator maxIter = max_element(cc.begin(),cc.end());
    if (maxIter != cc.end()){ 
         return *maxIter;               // not a good way either. but will work.
    } 
    else {
         return -1;                       // logically indicatting no value depends on implementation.
    }