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Updated on 2025-03-01

The use and difference between C# new and malloc

new keywords

  • The new keyword is used in C# to instantiate objects and allocate memory to them. It is one of the basic operations of object-oriented programming.
  • Use the new keyword to allocate memory on the managed heap while calling the object's constructor for initialization.
  • The new keyword will automatically handle the allocation and release of memory, and there is no need to manually manage memory.

Sample code:

MyClass obj = new MyClass(); // usenewKeyword instantiation object

malloc

  • malloc is a memory allocation function in C/C++ language, used to allocate a memory block of a specified number of bytes on the heap.
  • In C#, methods can be used to simulate the behavior of malloc.
  • The memory block allocated by malloc will not be automatically garbage collected and memory needs to be released manually, otherwise it may lead to memory leaks.

Sample code:

int* ptr = (int*)(sizeof(int)); // Use AllocHGlobal to simulate malloc*ptr = 10;
((IntPtr)ptr); // Manually release memory

It should be noted that in C#, it is usually recommended to use the new keyword for object instantiation and memory allocation, because it provides a higher level of memory management and automatic garbage collection. Low-level memory allocation methods such as malloc are generally used for interaction with unmanaged code or performance optimization in special cases. They need to be used with caution and ensure that the allocation and release of memory is properly managed.

The difference between C# new and malloc

The new keyword and malloc functions in C# are keywords and functions used to allocate objects or value types in memory, and there are some important differences between them.

  • Type: The new keyword is used to create an instance of a reference type, while the malloc function is used to allocate memory space for a value type.
  • Memory management: Objects created using the new keyword are managed by the Garbage Collector. The garbage collector automatically recognizes objects that are no longer in use and frees up the memory they occupy. The memory allocated using the malloc function needs to be manually released, and the allocated memory is released by calling the free function.
  • Exception handling: When creating an object using the new keyword, if there is insufficient memory or other errors occur, an OutOfMemoryException or other related exceptions will be raised. When using the malloc function to allocate memory, if the memory is insufficient, null will be returned, and the return value needs to be manually checked to handle the failure of memory allocation.
  • Object initialization: Objects created with the new keyword will automatically call the constructor after allocating memory to initialize the object's state. The memory space allocated using the malloc function will not automatically call the constructor and need to be initialized manually.
  • Managed Environment: The new keyword is used to create objects in a managed environment, which means that the life cycle of the object is managed by the garbage collector. The malloc function is used to allocate unmanaged memory spaces, which may be isolated from the managed environment and need to be managed and released manually.

In general, the new keyword is suitable for creating instances of reference types and memory is automatically managed by the garbage collector. The malloc function is suitable for allocating memory space of value types and requires manual management and freeing of memory. In C#, it is recommended to use the new keyword to create objects because it provides greater security and convenience and avoids the complexity of manually managing memory.

Operations done at the bottom of C# new keyword

In C#, using the new keyword can create a new object or overwrite members of the base class. At the bottom, the new keyword performs the following:

  • Memory allocation: The new keyword allocates memory space for objects on the heap. This involves allocating enough memory to the object on the heap to store its member variables and methods.
  • Member initialization: Objects created with the new keyword need to be initialized for member variables. This includes members of the base class and newly added members in the derived class. The initialization of the base class member will call the base class constructor, while the newly added members of the derived class can be initialized in the derived class constructor.
  • Calling the constructor: When creating an object with the new keyword, the constructor of the object will be called. The constructor is a special member method that is used to initialize the state of an object and perform necessary operations. In derived classes, constructors can ensure the correct initialization of base class members by calling the base class's constructor using the base keyword.

It should be noted that the specific operation of the new keyword will be affected by the compiler's optimization and the target platform. The compiler may make some optimizations to the new keyword, such as the usage of object pools or optimization of memory layout. Additionally, different .NET runtime implementations such as .NET Framework and .NET Core may have different implementation details.

In summary, the new keyword performs operations such as memory allocation, member initialization, and constructor calls on the underlying layer to create a new object and initialize its state. These operations ensure that the object's member variables and methods are properly initialized and provide the initial state required for the object's use.

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