Pointer types (C# Programming Guide)
In an unsafe context, a type may be a pointer type, a value type, or a reference type. A pointer type declaration takes one of the following forms:
type* identifier;
void* identifier; //allowed but not recommended
Any of the following types may be a pointer type:
sbyte, byte, short, ushort, int, uint, long, ulong, char, float, double, decimal, or bool.
Any enum type.
Any pointer type.
Any user-defined struct type that contains fields of unmanaged types only.
Pointer types do not inherit from object and no conversions exist between pointer types and object. Also, boxing and unboxing do not support pointers. However, you can convert between different pointer types and between pointer types and integral types.
When you declare multiple pointers in the same declaration, the * is written together with the underlying type only, not as a prefix to each pointer name. For example:
int* p1, p2, p3; // Ok
int *p1, *p2, *p3; // Invalid in C#
A pointer cannot point to a reference or to a struct that contains references because an object reference can be garbage collected even if a pointer is pointing to it. The GC does not keep track of whether an object is being pointed to by any pointer types.
The value of the pointer variable of type myType* is the address of a variable of type myType. The following are examples of pointer type declarations:
Example |
Description |
|---|---|
int* p |
p is a pointer to an integer |
int** p |
p is a pointer to pointer to an integer |
int*[] p |
p is a single-dimensional array of pointers to integers |
char* p |
p is a pointer to a char |
void* p |
p is a pointer to an unknown type |
The pointer indirection operator * can be used to access the contents at the location pointed to by the pointer variable. For example, consider the following declaration:
int* myVariable;
The expression *myVariable denotes the int variable found at the address contained in myVariable.
You cannot apply the indirection operator to a pointer of type void*. However, you can use a cast to convert a void pointer to any other pointer type, and vice versa.
A pointer can be null. Applying the indirection operator to a null pointer causes an implementation-defined behavior.
Be aware that passing pointers between methods can cause undefined behavior. Examples are returning a pointer to a local variable through an Out or Ref parameter or as the function result. If the pointer was set in a fixed block, the variable to which it points may no longer be fixed.
The following table lists the operators and statements that can operate on pointers in an unsafe context:
Operator/Statement |
Use |
|---|---|
* |
Performs pointer indirection. |
-> |
Accesses a member of a struct through a pointer. |
[] |
Indexed a pointer. |
& |
Obtains the address of a variable. |
++ and -- |
Increments and decrements pointers. |
+ and - |
Performs pointer arithmetic. |
==, !=, <, >, <=, and >= |
Compares pointers. |
stackalloc |
Allocates memory on the stack. |
fixed statement |
Temporarily fixes a variable so that its address may be found. |
C# Language Specification
For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.
See Also
Reference
Unsafe Code and Pointers (C# Programming Guide)
Pointer Conversions (C# Programming Guide)
Pointer Expressions (C# Programming Guide)
fixed Statement (C# Reference)
Boxing and Unboxing (C# Programming Guide)