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Lab_memory

CS225 - Data Structures

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If we run the program it may or may not complete without errors.

int main(){

int * arr = new int[100];

return arr[100];

}

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What happens if we run valgrind? �valgrind ./main

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Valgrind - a programming tool for memory debugging, memory leak detection, and profiling. 

We will always check for memory errors and leaks on your assignments unless specified

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int main(){

int * arr = new int[100];

return arr[100];

}

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Example 1

What is wrong with this code?

​

​

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int main(){

int * arr = new int[100];

return arr[100];

}

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Out-of-bounds access to heap, stack, and globals. This error occurs when you allocate some memory and then try to access a region outside your allocated space.

int main(){

int * arr = new int[100];

return arr[100];

}

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int main(){

int * arr = new int[100];

return arr[100];

}

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int main(){

int x;

cout << x << endl;

}

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Example 2 - Use of an uninitialized value.

int main(){

int * x = new int;

delete x;

delete x;

}

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Example 3 - Invalid free error

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Destructor

  • Destructors are usually used to deallocate memory and do other cleanup for a class object and its class members when the object is destroyed. �
  • A destructor is called for a class object when that object passes out of scope or is explicitly deleted.

class Animal{

Animal();

~Animal();

}

Animal::Animal(){}

​

Animal::~Animal(){}

​

Animal.cpp

Animal.h

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class A{

private:

int *n;

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public:

A(int n1);

~A();

};

A::A(int n1){

n = new int(n1);

}

A::~A(){

delete n;

}

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How will you change destructor if n was array of integers?

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class A{

private:

int *n;

​

public:

A(int n1);

~A();

};

A::A(int n1){

n = new int(n1);

}

A::~A(){

delete n;

}

​

How will you change destructor if n was array of integers?

delete[]

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int main(){

int * x = new int[6];

delete x;�}

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Example 4 - Mismatched free() / delete / delete []

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int main(){

int * arr = new int[10];

int * x = new int;

int * y;

arr[0] = *y;

delete arr;

delete x;

delete y;

return 0;

}

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​

Spot the errors!

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int main(){

int * arr = new int[10];

int * x = new int;

int * y;

arr[0] = *y; // y not initialized

delete arr; // Wrong delete, should be delete[] arr

delete x;

delete y; // Should not delete, not on heap return 0;

}

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Spot the errors (Solution)

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Tip: Valgrind output can get long

If necessary pipe the output of Valgrind to a file

valgrind ./exec &> log.txt

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Tip: Read the Doxygen before beginning!

Make sure you understand what the code base is supposed to do!

The Allocator class takes as input Students and Rooms

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Tip: Read the Doxygen before beginning!

Make sure you understand what the code base is supposed to do!

Students are loaded into Letter groups!

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Tip: Read the Doxygen before beginning!

Make sure you understand what the code base is supposed to do!

Rooms store collections of Letters and have a capacity

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