The Difference Between malloc and new

1. Memory Allocation and Initialization

Both malloc and new allocate memory on the heap, but:

• malloc only allocates memory without initialization.
• new allocates memory and initializes it.

Examples:

• new int(10) → Allocates an int and initializes it to 10.
• new int[10]() → Allocates an int array of size 10 and initializes all elements to 0.

2. Usage and Return Type

Code examples:

int *p1 = (int *)malloc(sizeof(int));  // malloc: cast required​
int *p2 = new int(2);                  // new: initializes single int to 2​
int *p3 = new int[100](0);             // new: array of 100 ints (all 0)

Execution output:

1​
2​
3

• malloc is a function:
• Requires specifying the number of bytes (e.g., malloc(100) for 100 bytes).
• Returns a void* pointer (needs explicit casting to the target type).
• new is an operator:
• Requires specifying the data type (not byte count).
• Returns a pointer of the specified type directly (no casting needed).

3. Error Handling and Underlying Logic

• malloc returns null if allocation fails.
• new throws a bad_alloc exception on failure (must be caught to check success).
• new internally calls operator_new, which uses malloc for allocation but adds initialization. For classes, this means calling the constructor.

4. Memory Deallocation

• Memory from malloc is freed with free().
• Memory from new is freed with:
• delete for single objects (e.g., delete p2;).
• delete[] for arrays (e.g., delete[] p3;).

5. Allocation Variants

• malloc has only one allocation method.
• new has four variants:

1. Ordinary new
2. const new
3. Placement new (allocates at a specific memory address)
4. nothrow new (returns null instead of throwing exceptions on failure)

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