vector causing system error/crash

[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.