Pointers and Memory Management Flashcards
What is a memory address?
A unique identifier for a location in memory where data is stored.
How is memory allocated when declaring a variable?
The system reserves memory space and updates the lookup table with its address.
What happens when you assign a value to a variable?
The system finds the variable in the lookup table, goes to the memory address, and stores the value.
What is a pointer?
A variable that stores the memory address of another variable.
How do you declare a pointer?
<datatype> *pointer_name;
## Footnote
Example: int *p; declares a pointer to an integer.
</datatype>
What does the & operator do?
It returns the memory address of a variable.
What does the * operator do when used with a pointer?
It dereferences the pointer to access the value stored at the memory address.
How do you assign a pointer to a variable’s address?
p = &variable;
What happens when you change the value at a pointer’s address?
The value stored in the original variable changes.
How do you print a pointer’s address in C?
Using %p in printf: printf(“Address: %p\n”, p);
What happens when you increment a pointer?
The pointer moves to the next memory location based on its data type size.
If x is a pointer to an int, what does x++ do?
It moves x to the next integer’s address (typically increasing by 4 bytes).
How are arrays and pointers related?
The array name is a pointer to the first element.
What is equivalent to array[i] using pointers?
*(array + i)
What happens when you assign an array to a pointer?
The pointer stores the address of the first element.
What is the output of this code?
char str[] = “Hello”;
char *p = str;
printf(“%s\n”, p);
“Hello”
What is a void pointer?
A pointer that can hold the address of any data type.
Why do you need to cast a void pointer before dereferencing?
Because its data type is unknown, so you must specify it.
How do you cast a void pointer to a char *?
(char *)p
Why is dynamic memory allocation needed?
To allocate memory at runtime when the size is unknown at compile time.
What function is used to allocate dynamic memory?
malloc()
What does malloc() return?
A pointer to the allocated memory (or NULL if allocation fails).
What happens if you forget to free memory allocated with malloc()?
A memory leak occurs.
How do you free dynamically allocated memory?
free(pointer);
What happens if you use a pointer after calling free() on it?
Undefined behavior; it becomes a dangling pointer.
What is a segmentation fault?
An error caused by accessing invalid memory.
What happens if you dereference an uninitialized pointer?
Undefined behavior, possibly a crash.
What is a dangling pointer?
A pointer that still references a memory location after it has been freed.
What is a wild pointer?
An uninitialized pointer that points to an unknown memory location.
Why must you always check if malloc() returns NULL?
To prevent accessing unallocated memory.
What should you always do after malloc()?
Check if the allocation was successful: if (p == NULL) { printf(“Memory allocation failed”); exit(1); }
What is a good practice before freeing memory?
Set the pointer to NULL after calling free().
What tool can help detect memory leaks?
valgrind
