Introduction to go language pointer

Preface

And Java and .NET Different programming languages ,Go Language provides programmers with the ability to control data structure pointers , however , Pointer operations are not possible .Go Language allows you to control the data structure of a specific set 、 Number of allocations and memory access mode , This is very important for building a well functioning system . The impact of pointers on performance is self-evident , If you want to do system programming 、 Operating system or network application , Pointers are an integral part .

The pointer （pointer） stay Go Language can be divided into two core concepts ：

• Type a pointer , Allows you to modify the data of this pointer type , You can pass data directly using pointers , Without copying data , Type pointers cannot be offset and operated .
• section , By the original pointer to the starting element 、 Element number and capacity composition .

Benefit from such constraints and splits ,Go The pointer type variable of language has the characteristics of efficient pointer access , There will be no pointer offset , Thus, the problem of illegally modifying key data is avoided . meanwhile , Garbage collection is also easier to retrieve and recycle pointers that will not be offset . Slicing has more powerful features than raw pointers , And safer . When the slice crosses the boundary , Downtime will be reported at runtime , And hit the stack , And the original pointer just crashes .

Know pointer address and pointer type

A pointer variable can point to the memory address of any value , The memory address of the value it points to is 32 and 64 Respectively occupied on bit machines 4 or 8 Bytes , The size of the occupied bytes is independent of the size of the value pointed to . When a pointer is defined and not assigned to any variable , Its default value is nil. Pointer variables are usually abbreviated to ptr.

return nil Indicates that null is returned , And JAVA Inside return null The way of writing is different , But the meaning is the same , So it feels awkward , In fact, although they all mean empty , however Go there nil Indicates a pointer .

Each variable has an address at run time , This address represents the location of the variable in memory .Go Used in languages before variable names add to & The operator （ Prefix ） To get the memory address of the variable （ Address operation ）, The format is as follows ：

ptr := &v    // v  The type of  T

among v The variable representing the address to be taken , Variable v Address usage variable for ptr Receive ,ptr The type of *T, It's called T Pointer type of ,* For the pointer .

Pointer actual usage , You can learn from the following example ：

Two variables are declared in the code , And used fmt.Printf It's a simple verb %p Print cat and str Memory address of variable , The value of the pointer is with 0x A set of data with a hexadecimal prefix .

Tips ： Variable 、 The relationship between pointer and address is ： Every variable has an address , The value of the pointer is the address .

Get the value that the pointer points to from the pointer

When using & Operator to get the address of a common variable and get the pointer of the variable , You can use * The operator , That is, the value of the pointer , The code is as follows ：

 Take the address operator & And value operators * It's a pair of complementary operators ,& Take out the address ,* Take the value pointed to by the address .

Variable 、 Pointer address 、 Pointer to the variable 、 Address fetch 、 The relationships and characteristics of values are as follows ：

• To get the address of a variable, use & The operator , You can get the pointer variable of this variable .
• The value of the pointer variable is the pointer address .
• The pointer variable can be accessed using * The operator , You can get the value of the original variable that the pointer variable points to .

Use the pointer to modify the value

You can not only take values through pointers , You can also modify the value .

* Operator as the right value , The meaning is to take the value of the pointer , As an lvalue , That is, on the left side of the assignment operator , Express a The variable that the pointer points to . In fact, to sum up ,* The fundamental meaning of an operator is to manipulate the variable that the pointer points to . When the operation is on the right , Is to take the value of the variable , When the operation is on the left , Is to set the value to the variable that you point to .

Another way to create a pointer ——new() function

Go The language also provides another way to create pointer variables , The format is as follows ：

new( type )

It's usually written like this ：

str := new(string)
*str = "Go Language course "
fmt.Println(*str)

new() Function to create a pointer to the corresponding type , The creation process allocates memory , The created pointer points to the default value .