go如何调用C动态库函数

package main


/*
#include <dlfcn.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#cgo LDFLAGS: -ldl

struct Hardware_API_Result {
   int  result;
   char json[256];
};


char* getSysTime(){
   //  手动加载指定位置的so动态库
	void* handle = dlopen("libhardwareInfo2.so", RTLD_LAZY);
	struct Hardware_API_Result (*getSysT)();

	//根据动态链接库操作句柄与符号，返回符号对应的地址
	getSysT = dlsym(handle, "get_system_time");

	//struct MidStruct midres;
	struct Hardware_API_Result r;
	r = getSysT();

	//static char* cj="404";  不能使用静态变量，多个线程调用，值会覆盖；测试：多次调用go中日志输出成乱码
	char * cj;
	cj = (char *)malloc(256);
	strcpy(cj,"404");
	//
	if(r.result==0){
	   strcpy(cj,r.json);
	}
	dlclose(handle);
	return cj;
}
int start4G(){
	void* handle = dlopen("libhardwareInfo2.so", RTLD_LAZY);
	int (*start4G)();
	start4G = dlsym(handle, "start_4g");
	int rv=start4G();
	dlclose(handle);
	return rv;
}

int ping(char* cip){
    void* handle = dlopen("libhardwareInfo2.so", RTLD_LAZY);
	struct Hardware_API_Result (*midFuncName)( char* );
    midFuncName = dlsym(handle, "ping");
	struct Hardware_API_Result midres;
    midres=midFuncName(cip);
	int rvi=midres.result;
    dlclose(handle);

    return rvi;
}


*/
import "C"
import (
	"fmt"
	"unsafe"
)


/*
获取系统时间
json 格式：{"local_time":2020-03-23  03:02:46.795268}
*/
func getSystime() string {
    //c中指针
	sip:=C.getSysTime()
	//转变为go字符串
	si:=C.GoString(sip)
	//释放c中指针
	C.free(unsafe.Pointer(sip))
	return  si
}
/*
启动4g,启动成功返回0
*/
func start4G() int{
	//c类型
	mrv:=C.start4G()
	//转换成go int类型
	rv:=int(mrv)
	return rv
}


/**
判断某ip可否ping通，值为0表示通
*/
func ping(ip string)int{
	cip := C.CString(ip)
	mrv:=C.ping(cip)
	rv:=int(mrv)
	C.free(unsafe.Pointer(cip))
	return rv
}

C.char  
C.schar (signed char)  
C.uchar (unsigned char)  
C.short  
C.ushort (unsigned short)  
C.int  
C.uint (unsigned int)  
C.long  
C.ulong (unsigned long)  
C.longlong (long long)  
C.ulonglong (unsigned long long)  
C.float  
C.double.   
  
  
unsafe.Pointer (void*)  
  
// Go string to C string  
func C.CString(string) *C.char  
  
var val []byte  
(*C.char)(unsafe.Pointer(&val[0]))