Runtime error when initializing multiple pointers

Question

This is probably just something I don't understand about c++, but why does this code give me a runtime error? If I don't initialize someInt2 or I don't specify that aClass has an int member, I don't get the error.

using namespace std;

class aClass
{
  int someint;
  public:
  aClass()
  {
    someint=4;
  }
};

int bFunc()
{
  return 4;
}


aClass aFunc()
{
  aClass class1=aClass();
  return class1;
}

int main()
{
  int * someInt2;
  *someInt2=bFunc();
  aClass * thisClass;
  cout << "Got here" << endl;
  *thisClass=aFunc();
  cout << "Not here" << endl;
  return 0;
}

Puppy · Accepted Answer · 2012-08-18 17:56:30Z

1

int * someInt2;
*someInt2=bFunc();

Undefined behaviour. You didn't make someInt2 point anywhere meaningful.

Edit: "Appearing to function correctly" is one of the possible things that "undefined behaviour" can be.

edited Aug 18, 2012 at 17:56

answered Aug 18, 2012 at 16:47

Puppy

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2 Comments

user1609012 Over a year ago

May I then ask why the function will run smoothly if I define aClass simply as class aClass{}; ?

jrok Over a year ago

Because apearing to run smoothly is one of the possible outcomes of running a program that contains undefined behaviour. Your program is ill-formed and the compiler isn't required to emit sensible code.

mathematician1975 · Accepted Answer · 2012-08-18 16:49:36Z

1

 int * someInt2;

is an uninitialised pointer, and yet you are trying to assign a value to what it points to. You need to allocate some memory or simply use a int variable to store the return value of the function.

answered Aug 18, 2012 at 16:49

mathematician1975

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