golang c 函数指针

Introduction

Go is a programming language that provides support for writing C functions and working with function pointers. In this article, we will explore the concept of function pointers in Go and how they can be used to enhance the functionality and flexibility of your code.

Function Pointers in Go

Function pointers in Go are similar to function pointers in C. They allow you to refer to a function by its memory address, which can then be used to call the function at a later point in time. This is particularly useful when you want to pass functions as arguments to other functions or store the address of a function in a data structure.

Declaring and Using Function Pointers

To declare a function pointer in Go, you need to specify the function signature, including the return type and parameter types. Here's an example:

type MyFunction func(int) int

In this example, we define a new type called MyFunction, which represents a function that takes an integer parameter and returns an integer value.

You can then declare a variable of type MyFunction and assign it a function:

var fn MyFunction = myFunctionImpl

In this case, we assign the address of the function myFunctionImpl to the variable fn. We can now call the function using the variable:

result := fn(42)

This will invoke the function myFunctionImpl with the argument 42 and store the result in the variable result.

Passing Function Pointers as Arguments

One of the main advantages of using function pointers in Go is the ability to pass functions as arguments to other functions. This allows you to create more flexible and reusable code.

Here's an example that demonstrates this:

func applyFunction(fn MyFunction, value int) int {
    return fn(value)
}

func increment(x int) int {
    return x + 1
}

func double(x int) int {
    return x * 2
}

func main() {
    result := applyFunction(increment, 10)
    fmt.Println(result) // Output: 11

    result = applyFunction(double, 5)
    fmt.Println(result) // Output: 10
}

In this example, we have defined three functions: applyFunction, increment, and double. The applyFunction function takes a function pointer as its first argument and applies the function to the second argument.

In the main function, we call applyFunction twice with different functions and values. The output shows the results of applying the respective functions to the given values.

Storing Function Pointers in Data Structures

Function pointers can also be stored in data structures such as arrays, slices, or maps. This can be useful when you need to dynamically select and call different functions based on certain conditions.

Here's an example that demonstrates storing function pointers in a map:

var functionMap = map[string]MyFunction{
    "increment": increment,
    "double":    double,
}

func applyFunctionByName(name string, value int) int {
    fn := functionMap[name]
    if fn != nil {
        return fn(value)
    }
    return 0
}

func main() {
    result := applyFunctionByName("increment", 10)
    fmt.Println(result) // Output: 11

    result = applyFunctionByName("double", 5)
    fmt.Println(result) // Output: 10
}

In this example, we define a map called functionMap that associates function names with their respective function pointers. The applyFunctionByName function takes a name and a value as input and applies the corresponding function to the value.

The main function demonstrates how to use the applyFunctionByName function to dynamically select and call different functions based on the provided name.

Conclusion

Function pointers in Go provide a powerful mechanism for working with functions at run-time. They allow you to pass functions as arguments, store them in data structures, and dynamically select and invoke different functions. Understanding how to use function pointers can greatly enhance the flexibility and extensibility of your Go code.