vector causing system error/crash

[babygal]

I am using vector in my code but when application is running it causes system error/crash.
Code in .h file :

#include <vector>
using namespace std;
 
bool callVector(vector<float>&);
void func();
 
vector <float> vectorname;

#include <vector>
using namespace std;

bool callVector(vector<float>&);
void func();

vector <float> vectorname;

To copy to clipboard, switch view to plain text mode 

Code in .cpp file:

void myClass::func()
{
    if(!callVector(vectorname))
    {
     qDebug() << " vector error" ;
     } 
    else
    {
       qDebug()<<"vector success" ;
       qDebug()<<"vector [0]" : << vectorname[0]; //**system error/crash HERE **
    }
}

void myClass::func()
{
    if(!callVector(vectorname))
    {
     qDebug() << " vector error" ;
     } 
    else
    {
       qDebug()<<"vector success" ;
       qDebug()<<"vector [0]" : << vectorname[0]; //**system error/crash HERE **
    }
}

To copy to clipboard, switch view to plain text mode 

System error/crash at line 10 in .cpp.
Application output:

vector success
.exe exited with code -1073741819