Programming Forums > Application Development > C++

can342man · Apr 20th, 2006, 2:21 PM

I have seen a lot of debate on wheather to use arrays or vectors for passing arrays in functions. I have a simple program here that does not quite seem to work properly as what I intended. The goal is to take the arrays from f1() and f2() and pass all the elements to the main where the elements are added togethor. I get a "segmentation fault" error.

How would I use vectors as an alternate to arrays?

(Toggle Plain Text)

#include <iostream>
#include <cmath>
using namespace std;

double f1(int a);
double f2(int b);

int main()
{
	int a1, b1;
	double numTot[6];

	f1(a1);
	f2(b1);

	// sum of 2 arrays element by element
	for(int k=0; k<=5; k++)
	{
		numTot[k] = f1(a1) + f2(b1);
		cout << "numTot[" << k << "]: " <<  numTot[k] << endl;
	}
	return 0;
}

double f1(int a2)
{
	double num1[6];

	// place 6 numbers in array num1
	for(int t=0; t<=5; t++)
	{
		num1[t] = t+1.0;
		cout << "num1[" << t << "]: " << num1[t] << endl;
	}
	return num1[a2];
}

double f2(int b2)
{
	double num2[6];

	// place 6 numbers in array num2
	for(int j=0; j<=5; j++)
	{
		num2[j] = j+2.0;
		cout << "num2[" << j << "]: " <<  num2[j] << endl;
	}
	return num2[b2];
}

Thanks if anyone can clarify this.

:banana:

mikaoj · Apr 20th, 2006, 3:31 PM

Use a pointer.
And pass the array through the function.

(Toggle Plain Text)

void func(double *table, int len)

Cache · Apr 20th, 2006, 3:57 PM

The seg fault is caused by a1 and b1 being used to index an array before they have been initialized to a value within the valid range.

Here is a vector version of your code. I've not changed any logic, so if the output isn't what you expected, that's your fault

(Toggle Plain Text)

#include <iostream>
#include <vector>

using namespace std;

// TODO: Const correctness.

double f1(int a, double arg2);

int main()
{
	try
	{
		// a1 and b1 must be initialized to some number
		// withing the bounds of vecNum.
		int a1 = 0, b1 = 0;
		vector<double> vecNumTot( 6, 0 );

		f1( a1, 1.0 );
		f1( b1, 2.0 );
		
		// sum of 2 vector element by element
		vector<double>::iterator i = vecNumTot.begin();
		for( int j = 0; i != vecNumTot.end(); ++i, ++j )
		{
			*i = f1( a1 , 1.0 ) + f1( b1, 2.0 );
			cout << "vecNumTot[" << j << "]: " <<  *i << endl;
		}
	} catch ( std::out_of_range& )
	{
		// TODO: Error hadnling.
		
		// NOTE: This try/catch block isn't needed if
		// there's no chance a1/b1 are passed to
		// f1 with a value exceeding vecNum.end().
	}
	
	cin.get();
	return 0;
}

double f1( int a, double arg2 )
{
	vector<double> vecNum( 6, 0 );

	// place 6 numbers in int vector vecNum1
	vector<double>::iterator i = vecNum.begin();
	for( int j = 0; i != vecNum.end(); ++i, ++j )
	{
		*i = j + arg2;
		cout << "vecNum[" << j << "]: " << *i << endl;
	}
	
	// If 'a' is out of range, an exception will
	// be thrown.
	return vecNum.at( a );
}

Apr 20th, 2006, 2:21 PM	#1
can342man Newbie Join Date: Jan 2006 Location: London, Ontario, Canada Posts: 16 Rep Power: 0	Arrays or Vectors? I have seen a lot of debate on wheather to use arrays or vectors for passing arrays in functions. I have a simple program here that does not quite seem to work properly as what I intended. The goal is to take the arrays from f1() and f2() and pass all the elements to the main where the elements are added togethor. I get a "segmentation fault" error. How would I use vectors as an alternate to arrays? (Toggle Plain Text) #include <iostream> #include <cmath> using namespace std; double f1(int a); double f2(int b); int main() { int a1, b1; double numTot[6]; f1(a1); f2(b1); // sum of 2 arrays element by element for(int k=0; k<=5; k++) { numTot[k] = f1(a1) + f2(b1); cout << "numTot[" << k << "]: " << numTot[k] << endl; } return 0; } double f1(int a2) { double num1[6]; // place 6 numbers in array num1 for(int t=0; t<=5; t++) { num1[t] = t+1.0; cout << "num1[" << t << "]: " << num1[t] << endl; } return num1[a2]; } double f2(int b2) { double num2[6]; // place 6 numbers in array num2 for(int j=0; j<=5; j++) { num2[j] = j+2.0; cout << "num2[" << j << "]: " << num2[j] << endl; } return num2[b2]; } #include <iostream> #include <cmath> using namespace std; double f1(int a); double f2(int b); int main() { int a1, b1; double numTot[6]; f1(a1); f2(b1); // sum of 2 arrays element by element for(int k=0; k<=5; k++) { numTot[k] = f1(a1) + f2(b1); cout << "numTot[" << k << "]: " << numTot[k] << endl; } return 0; } double f1(int a2) { double num1[6]; // place 6 numbers in array num1 for(int t=0; t<=5; t++) { num1[t] = t+1.0; cout << "num1[" << t << "]: " << num1[t] << endl; } return num1[a2]; } double f2(int b2) { double num2[6]; // place 6 numbers in array num2 for(int j=0; j<=5; j++) { num2[j] = j+2.0; cout << "num2[" << j << "]: " << num2[j] << endl; } return num2[b2]; } Thanks if anyone can clarify this. :banana: __________________ Greatness courts failure and solitude. --- Anonymous

Apr 20th, 2006, 3:31 PM	#2
mikaoj Programmer Join Date: Aug 2005 Location: Norway Posts: 56 Rep Power: 0	Use a pointer. And pass the array through the function. (Toggle Plain Text) void func(double table, int len) void func(double table, int len) __________________ Heh. Last edited by mikaoj; Apr 20th, 2006 at 3:44 PM.

Apr 20th, 2006, 3:57 PM	#3
Cache Hobbyist Join Date: Sep 2005 Posts: 256 Rep Power: 3	The seg fault is caused by a1 and b1 being used to index an array before they have been initialized to a value within the valid range. Here is a vector version of your code. I've not changed any logic, so if the output isn't what you expected, that's your fault (Toggle Plain Text) #include <iostream> #include <vector> using namespace std; // TODO: Const correctness. double f1(int a, double arg2); int main() { try { // a1 and b1 must be initialized to some number // withing the bounds of vecNum. int a1 = 0, b1 = 0; vector<double> vecNumTot( 6, 0 ); f1( a1, 1.0 ); f1( b1, 2.0 ); // sum of 2 vector element by element vector<double>::iterator i = vecNumTot.begin(); for( int j = 0; i != vecNumTot.end(); ++i, ++j ) { i = f1( a1 , 1.0 ) + f1( b1, 2.0 ); cout << "vecNumTot[" << j << "]: " << i << endl; } } catch ( std::out_of_range& ) { // TODO: Error hadnling. // NOTE: This try/catch block isn't needed if // there's no chance a1/b1 are passed to // f1 with a value exceeding vecNum.end(). } cin.get(); return 0; } double f1( int a, double arg2 ) { vector<double> vecNum( 6, 0 ); // place 6 numbers in int vector vecNum1 vector<double>::iterator i = vecNum.begin(); for( int j = 0; i != vecNum.end(); ++i, ++j ) { i = j + arg2; cout << "vecNum[" << j << "]: " << i << endl; } // If 'a' is out of range, an exception will // be thrown. return vecNum.at( a ); } #include <iostream> #include <vector> using namespace std; // TODO: Const correctness. double f1(int a, double arg2); int main() { try { // a1 and b1 must be initialized to some number // withing the bounds of vecNum. int a1 = 0, b1 = 0; vector<double> vecNumTot( 6, 0 ); f1( a1, 1.0 ); f1( b1, 2.0 ); // sum of 2 vector element by element vector<double>::iterator i = vecNumTot.begin(); for( int j = 0; i != vecNumTot.end(); ++i, ++j ) { i = f1( a1 , 1.0 ) + f1( b1, 2.0 ); cout << "vecNumTot[" << j << "]: " << i << endl; } } catch ( std::out_of_range& ) { // TODO: Error hadnling. // NOTE: This try/catch block isn't needed if // there's no chance a1/b1 are passed to // f1 with a value exceeding vecNum.end(). } cin.get(); return 0; } double f1( int a, double arg2 ) { vector<double> vecNum( 6, 0 ); // place 6 numbers in int vector vecNum1 vector<double>::iterator i = vecNum.begin(); for( int j = 0; i != vecNum.end(); ++i, ++j ) { i = j + arg2; cout << "vecNum[" << j << "]: " << i << endl; } // If 'a' is out of range, an exception will // be thrown. return vecNum.at( a ); }

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Programming Forums > Application Development > C++

Arrays or Vectors?