package main

// #include <stdlib.h>
import "C"

import (
    "fmt"
    "syscall"
    "unsafe"
)

func main() {
    kernel := syscall.NewLazyDLL("Kernel32.dll")
    defer syscall.CloseHandler(syscall.Handle.(kernel.Handle()))
    volume := kernel.NewProc("GetVolumePathNameA")
    char := C.CString("D:")
    defer C.free(unsafe.Pointer(char))
    n := make([]byte,254)
    _,_,err := volume.Call(uintptr(unsafe.Pointer(char)),uintptr(unsafe.Pointer(&n[0])),254)
    fmt.Println(err)
    fmt.Println(string(n))
}

当我想使用C.free()释放申请的变量的时候.提示没有此函数.
后来百度无果,Google链接到官方文档看到下面这段解释

// Go string to C string
// The C string is allocated in the C heap using malloc.
// It is the caller's responsibility to arrange for it to be
// freed,such as by calling C.free (be sure to include stdlib.h
// if C.free is needed).
func C.CString(string) *C.char

// C string to Go string
func C.GoString(*C.char) string

// C data with explicit length to Go string
func C.GoStringN(*C.char,C.int) string

// C data with explicit length to Go []byte
func C.GoBytes(unsafe.Pointer,C.int) []byte

所以使用C.free的时候必须要 include