Qt program seg faults when I try to insert a pair into a map

Question

I am working on my first Qt application, widget really, and I am getting a segfault when I try to fill up a standard library map with a <int, QString> pair. My goal is to fill the map with int keys and QString values. I don't know if pair is the best way to do this, so any advice would be great.

Here is the only source file besides the main.

#include "linuxtips.h"
#include "ui_linuxtips.h"

LinuxTips::LinuxTips(QWidget *parent) :
  QWidget(parent),
  ui(new Ui::LinuxTips)
{
  loadRandTip();
  ui->setupUi(this);
}

LinuxTips::~LinuxTips()
{
  delete ui;
}

void LinuxTips::on_learnMore_clicked()
{

}

void LinuxTips::on_viewAll_clicked()
{

}

void LinuxTips::loadRandTip()
{
  int i = 0;
  std::map<int, QString>::iterator it;

  QString line;
  QFile inputFile(":/tipFile.txt");
  inputFile.open(QIODevice::ReadOnly);

  QTextStream in(&inputFile);
  do{
    line = in.readLine();
  //  this->TipMap.insert(it, std::pair<int, QString >(i,line));
    i++;
  }while(!in.atEnd());
}

If I uncomment this->TipMap.insert(it, std::pair<int, QString >(i,line)); then it will run. Since it's a seg fault I'm sure its a memory overflow or null pointer, but I'm just not sure what it is. Thanks for any help.

Answer 1

I'm going to assume that your crash is due to these lines:

std::map<int, QString>::iterator it;
this->TipMap.insert(it, std::pair<int, QString >(i,line));

You're attempting to insert into a map using an invalid (uninitialized) iterator. Are you running this in debug or release? You should get an assertion in debug.