Seg Fault: Unknown Cause [closed] - c++

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I keep seg faulting. I have no idea why. Tried printing out an "ok" statement every few lines to show me where the error lay, but it seg faults before printing out even the first one. I think it is getting stuck possibly in the operator overload, or perhaps between some of the function calls, but that wouldn't explain why it doesn't even print out a single "ok" statement
#include <iostream>
#include <cstdlib>
#include <vector>
using namespace std;
class isprime{
public:
isprime();
void start(int thing);
bool test(int target);
void check(int x);
void checktwo(int xtwo);
int operator()(int p);
private:
void path(int targ);
vector<int> testing;
int b;
};
int main ()
{
int given;
while(cin>>given)
{
isprime Begin;
Begin.start(given);//check input as long as there is input
}
return 0;
}
void isprime::start(int thing)
{
if(test(thing) == 1)
{
cout<<thing<<" is a prime number.";
}
else
{
check(thing);
}
}
isprime::isprime()
{
testing[0] = {2};
b = 0;
}
void isprime::check(int x)//checks if input is prime, and sets up next step if so
{
int s;
if(x == 0 || x == 1 || x == -1 || x == 2 || x == -2)
{
cout<<x<<" is a prime number.";
}
else
{
for(int i = 2; i < x; i++)
{
s = x % i;
if(s == 0)
{
b = 1;
break;
}
}
if(s != 0)
{
cout<<x<<" is a prime number.";
}
path(x);
}
}
bool isprime::test (int target)//see if input is already in list
{
for(int i = 0; i < testing.size(); i++)
{
if(target == testing[i])
{
return 1;
}
}
if(int i = testing.size() && target != testing[i])
{
return 0;//if not in list, must test whether it is prime
}
}
void isprime::path(int targ)
{
int y = testing.back() + 1;
while(y != targ)//find all primes between list end and input
{
checktwo(y);
y++;
}
testing.push_back(targ);//add prime input to vector
int storage = testing.size();//remember size
int z = targ + 1;
while(b = 1)//find the next prime while the target isn't prime
{
checktwo(z);
if(testing.size() != storage)//if the size changed, the next prime has been found
{
break;
}
z++;
}
}
void isprime::checktwo(int xtwo)//modified check function to add prime numbers between the vector end and the input to the vector
{
int s;
if( xtwo == -2 || xtwo == -1 || xtwo == 0 || xtwo == 1 || xtwo == 2)
{
testing.push_back(xtwo);
}
else
{
for(int i = 2; i < xtwo; i++)
{
s = xtwo % i;
if(s == 0)
{
break;
}
}
if(s != 0)
{
testing.push_back(xtwo);
}
}
}
int operator()(int p)
{
test(p);//calls a private member function to expand list of prime numbers (test)
}

Answer 1

Here's the problem:
isprime::isprime()
{
testing[0] = {2}; //<<---------- here
b = 0;
}
At this point size of "testing" is zero. Testing is std::vector, you haven't initialized its size in constructor, so any attempt to access any index of testing will crash the program. (well, it is "undefined behavior", but it'll crash in your case). Because this happens in constructor, program crashes when it enters "main()".