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;

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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 **
    }
}

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

vector success
.exe exited with code -1073741819

[ChrisW67]

Do you ever add anything to the vector?

[Zlatomir]

This line:

vector <float> vectorname;

vector <float> vectorname;

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Creates an empty vector of floats (and you try to access the first of them)
If you create empty vector you can use the push_back(...) member function to add elements to that vector

Or use it like this:

vector <float> vectorname(10); //this construct a vector of floats with 10 elements

vector <float> vectorname(10); //this construct a vector of floats with 10 elements

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Some documentation for std::vector
Note that the operator[] doesn't check if the number you write there is in vectorname range, you have to make sure that you "stay" in range (else you get an error), you have the at() member function that checks that.

Or you can use QVector instead, documentation for QVector or QList

[babygal]

Do you ever add anything to the vector?

Yes. Contents are added into the vector container. The size is supposed to be around 2000 . But what I get , the size amounts to around 50 000 000 .

[Zlatomir]

Then show us the code where you add elements to the vector, and also the error you get might be useful (if you run the debug build you might get a "nicer" error message)

[babygal]

using push_back(.....)

[ChrisW67]

In the absence of your actual code this is what people assume you are doing:

#include <iostream>
#include <vector>
using namespace std;
 
bool callVector(vector<float>& v)
{
    v.push_back(1.2);
    v.push_back(2.3);
    return true;
}
 
int main(int argc, char *argv[])
{
    vector<float> vectorname;
    cout << vectorname.size() << endl;
 
    // The following line is probably what you are doing
    // There is no element 0 and ranges are not checked
    // cout << "vector [0]\t" << vectorname[0]; //**system error/crash HERE **
 
    bool res = callVector(vectorname);
    cout << res << "\t" << vectorname.size() << endl;
 
    // This works now the vector has something in it
    cout << "vector [0]\t" << vectorname[0];
}

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

bool callVector(vector<float>& v)
{
    v.push_back(1.2);
    v.push_back(2.3);
    return true;
}

int main(int argc, char *argv[])
{
    vector<float> vectorname;
    cout << vectorname.size() << endl;

    // The following line is probably what you are doing
    // There is no element 0 and ranges are not checked
    // cout << "vector [0]\t" << vectorname[0]; //**system error/crash HERE **

    bool res = callVector(vectorname);
    cout << res << "\t" << vectorname.size() << endl;

    // This works now the vector has something in it
    cout << "vector [0]\t" << vectorname[0];
}

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Are you returning true from your callVector() routine when you should not perhaps?

[babygal]

The code :
.h

#include <vector>
using namespace std; 
 
bool callVector(vector<float>&);
void func(); 
 
vector <float> vectorname;
QString filename = "vector.txt";
QFile file(filename);
QString val;
float v;

#include <vector>
using namespace std; 

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

vector <float> vectorname;
QString filename = "vector.txt";
QFile file(filename);
QString val;
float v;

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.cpp

void myClass::func(){   
 if(!callVector(vectorname))  
  {    
  qDebug() << " vector error" ;  
  }   
  else   
  {       
  qDebug()<<"vector success" ;      
  }  
 if (file.open(QIODevice::WriteOnly | QIODevice::Truncate))
   {
         for ( int i =0; i<vectorname.size() ; i++)
         {
              v = vectorname.at(i);          //system crash here 
              val = QString::number(v);
              qDebug()<< "val" << val;
              char *valtoAsciidata = val.toAscii().data();
              file.write(valtoAsciidata);
 
 
         }
            qDebug()<<"front =" << vectorname.front();
            qDebug()<<"back ="  << vectorname.back();
            qDebug()<< "vector write finish!:" << "success";
            file.close();
 
 
   }
   else
   {
       qDebug()<<"error write vector.txt file";
   }
}

void myClass::func(){   
 if(!callVector(vectorname))  
  {    
  qDebug() << " vector error" ;  
  }   
  else   
  {       
  qDebug()<<"vector success" ;      
  }  
 if (file.open(QIODevice::WriteOnly | QIODevice::Truncate))
   {
         for ( int i =0; i<vectorname.size() ; i++)
         {
              v = vectorname.at(i);          //system crash here 
              val = QString::number(v);
              qDebug()<< "val" << val;
              char *valtoAsciidata = val.toAscii().data();
              file.write(valtoAsciidata);


         }
            qDebug()<<"front =" << vectorname.front();
            qDebug()<<"back ="  << vectorname.back();
            qDebug()<< "vector write finish!:" << "success";
            file.close();


   }
   else
   {
       qDebug()<<"error write vector.txt file";
   }
}

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The system crash with error as below when debugging:

<Signal received>
The inferior stopped because it received a signal from the Operating System
Signal name : SIGSEGV
Signal meaning : Segmentation fault

The callVector is an API and it is called if dll is loaded. The code is in another program and the code is currently not transparent to me.

The qDebug() returns "vector success" message when callVector is called in my program.

[ChrisW67]

Are you absolutely sure that the callVector function is expecting a std::vector and not just space for a a plain old array of floats (i.e a float*)? Is vectorname.size() sensible when callVector returns? When the seg fault occurs what is the value of i?

If you have the API prototype correct then you need to speak to the author or provider of the DLL.

[babygal]

Q: "When the seg fault occurs what is the value of i?"
A : When the segmentation fault occurs, the value of i is always 0.