Memory Allocation in Functions

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Questions and Answers

In the provided code snippet, what is the primary reason for the memory leak?

The `malloc` function fails to allocate memory, resulting in a null pointer.

The program attempts to write data beyond the bounds of the allocated memory block.

The `free` function is called prematurely, deallocating memory that is still in use.

The allocated memory's address is assigned to a local pointer variable within the `allocate` function, which is not reflected in the calling function. (correct)

What is the purpose of passing a double pointer (e.g., `Card** newCardObject`) to the `createCard` function?

To improve the performance of memory allocation by directly accessing the memory address.

To create a local copy of the `Card` object within the function.

To allow the function to modify the original `Card` pointer in the calling function, enabling it to point to the newly allocated `Card` object. (correct)

To pass a read-only reference to the `Card` object, preventing modifications.

Which of the following is the correct way to compile a C program named `a1.c` into an executable named `a1` with debugging information for use with Valgrind or GDB?

`gcc a1.c -o a1 -debug`

`gcc a1.c -o a1 -g` (correct)

`gcc a1.c -o a1 -v`

`gcc a1.c -o a1`

Why is it necessary to pass the address of a variable to a function when the goal is to modify its original value?

Passing by value creates a copy, and modifications to the copy do not affect the original variable. (B) Signup and view all the answers

Which of the following best describes what Valgrind is primarily used for?

To debug memory-related errors, such as memory leaks and invalid memory access. (C) Signup and view all the answers

In the `allocate` function example, what is the purpose of using `int** p` as the parameter type?

To allow the function to modify the address stored in the pointer variable <code>array</code> in <code>main</code>. (B) Signup and view all the answers

What should you look for in Valgrind's output to determine if your program has any memory leaks?

The ERROR SUMMARY and LEAK SUMMARY sections. (B) Signup and view all the answers

If the `allocate` function was incorrectly defined as `void allocate(int* p, int len)`, what would be the consequence when called from `main`?

The <code>array</code> pointer in <code>main</code> would not be updated with the address of the allocated memory. (A) Signup and view all the answers

Consider a scenario where you want a function to both allocate memory for an array of floats and return the size of the allocated array. What parameters should the allocation function take?

A double pointer to a float, <code>float** arr</code>, and a pointer to an integer for the size, <code>int* size</code>. (A) Signup and view all the answers

Why is setting a pointer to `NULL` important before allocating memory to it?

It initializes the pointer to a known safe value, preventing it from pointing to a random memory location. (C) Signup and view all the answers

In the given code snippet, what is the initial value of the pointer `array` in the `main` function?

<code>NULL</code> (or 0). (D) Signup and view all the answers

Why does the `allocate` function, as implemented in the code, fail to modify the `array` pointer in the `main` function?

The <code>allocate</code> function modifies its local copy of the pointer, not the original pointer in <code>main</code>. (B) Signup and view all the answers

What is the size of the memory block (in bytes) that `malloc` attempts to allocate within the `allocate` function, assuming a 64-bit system?

80 bytes. (B) Signup and view all the answers

If the `allocate` function were to correctly modify the `array` pointer in `main`, what would be the value of `array` after the `allocate` function returns?

The starting address of the allocated memory block. (C) Signup and view all the answers

To fix the given code so that the `array` pointer in `main` is correctly updated by the `allocate` function, which of the following changes should be made?

Change the function signature to <code>void allocate(int** p, int len)</code> and dereference <code>p</code> with <code>*p = malloc(sizeof(int)*len);</code>. (C) Signup and view all the answers

What is the initial value stored in the variable `array` at memory address `05fd` before the `allocate` function is called?

<code>NULL</code>, which typically represents the integer value <code>0</code>. (D) Signup and view all the answers

Inside the `allocate` function, what does `p` represent?

The memory address of the <code>array</code> variable in the calling function. (D) Signup and view all the answers

What action does the line `p = malloc(sizeof(int)arrLen);` perform inside the `allocate` function?

It allocates memory and stores the starting address in the variable that <code>p</code> points to. (C) Signup and view all the answers

What does Valgrind's 'definitely lost' memory block status indicate?

The program is leaking memory, and it needs to be fixed. (B) Signup and view all the answers

If `malloc` returns the memory address `f23c`, what happens to the value stored at the memory address `05fd`?

The value at <code>05fd</code> is replaced by <code>f23c</code>. (A) Signup and view all the answers

If Valgrind reports 'indirectly lost' memory blocks, what is the recommended first step?

Fix the 'definitely lost' memory leaks first. (D) Signup and view all the answers

What is the value of `array` after the `allocate` function returns to `main()`?

The memory address of the newly allocated block, e.g. <code>f23c</code>. (C) Signup and view all the answers

What potential issue does the code `p = malloc(sizeof(int)arrLen);` not address directly?

All of the above. (D) Signup and view all the answers

What is the most likely cause of 'possibly lost' memory blocks reported by Valgrind?

The program uses pointers in unusual ways, pointing into the middle of allocated blocks. (B) Signup and view all the answers

According to the Valgrind output `total heap usage: 175 allocs, 175 frees... All heap blocks were freed`, what can be concluded about memory leaks?

There are no memory leaks detected. (A) Signup and view all the answers

Why is passing the address of a pointer (`int** p`) necessary in the `allocate` function to modify the original `array` variable?

It provides a way for the function to change the memory address stored in the original pointer variable. (A) Signup and view all the answers

If a C program allocates memory using `malloc` but forgets to `free` it, what kind of memory error will Valgrind most likely report?

'Definitely lost' (B) Signup and view all the answers

In a scenario where `arrLen` is 10 on a 64-bit system, what is the size in bytes of the memory block allocated by `malloc`?

80 bytes (B) Signup and view all the answers

Based on the Valgrind output, what is the primary issue identified in the `tree1` program?

The program has memory leaks, specifically 'definitely lost' and 'indirectly lost' memory. (B) Signup and view all the answers

In the `StructListDemo` Valgrind output, what does 'Invalid write of size 8' suggest?

The program is trying to write 8 bytes of data beyond the allocated memory block. (D) Signup and view all the answers

What does the line `Address 0x4a25d10 is 0 bytes inside a block of size 1 alloc'd` indicate in the `StructListDemo` Valgrind output?

The program is allocating a block of memory of size 1, which is too small to hold the data being written. (A) Signup and view all the answers

If Valgrind reports 'still reachable' memory, what does this typically imply?

The program has allocated memory that can still be accessed through existing pointers, but it was not explicitly freed before the program exited. (C) Signup and view all the answers

Why is it important to rerun Valgrind with the `--leak-check=full` flag when memory leaks are suspected?

To provide more detailed information about the location and nature of the memory leaks. (C) Signup and view all the answers

Flashcards

Dynamic Memory Allocation

The process of requesting memory from the heap during program execution, typically using malloc.

NULL Pointer

A special pointer value that indicates it doesn't point to any valid memory address, often represented as 0.

Function Parameter Passing

When a function is called, the arguments are passed to its parameters, which can be local copies.

malloc() Function

A library function in C that allocates a specified number of bytes from the heap and returns a pointer to the allocated memory.