How to return array of C struct from C function to go?

Question

I have a C function which will return an array of structure to go function. How can I receive the array of structure and interpret or cast to go structure?

Here is the code snippet

typedef struct student{  
    nameStruct name;  
    addressStruct address;  
} studentStruct;

typedef struct name{
    char firstName[20];
    char lastName[20];
} nameStruct;

typedef struct address{
    char location[40];
    int    pin;
}addressStruct;


student* getAllStudents(){
   //Allocate memory for N number of students
   student *pStudent= (struct student*)(N* sizeof(struct student));
   //populate the array
   return pStudent;
}

I need to get the pStudent array in my go code

package main

/*
#cgo CFLAGS: -I.
#cgo LDFLAGS: -L. -lkeyboard
#include "keyboard.h"
*/
import "C"
import (
    "fmt"
)

type student struct {
    name string
    ID int
}

func main() {
    s := student{} //Need to know how to decide the length of the struct array
    s = C.getAllStudents() //?????


}

Can some one help me with code snippet?

There's a lot of missing functionality here, covering a lot of basic areas. What part are you asking about? — Mr_Pink
– Mr_Pink, Commented Oct 12, 2016 at 20:14
what is the best way of casting C structure into Go structure? considering there can be different data types in the C structure. — user3218590
– user3218590, Commented Oct 13, 2016 at 6:19
If the data types are different, you need to copy/convert those to their respective fields. For example, Go strings are not the same as C strings, so you can't "cast" those, you need to copy the characters from the C char* to the Go string — Mr_Pink
– Mr_Pink, Commented Oct 13, 2016 at 12:52
I am aware of that, that's why I was looking for any other short cut which can directly cast or map C struct to Golang struct — user3218590
– user3218590, Commented Oct 14, 2016 at 5:27
I have added a complex C struct studentStruct in my original post. Can some one add a code snippet to interpret this C struct in Go code? — user3218590
– user3218590, Commented Oct 16, 2016 at 15:37

Mohanson · Accepted Answer · 2016-10-13 08:01:36Z

1

You could use the out paramters, and the way for C struct -> Go struct is thus:

package main

/*
#include <stdlib.h>

typedef struct Point{
    float x;
    float y;
}Point;

void GetPoint(void **ppPoint) {
   Point *pPoint= (Point *)malloc(sizeof(Point));
   pPoint->x=0.5f;
   pPoint->y=1.5f;
   *ppPoint = pPoint;
}
*/
import "C"

import "unsafe"

type Point struct {
    x float32
    y float32
}

func main() {
    var ppoint unsafe.Pointer
    C.GetPoint(&ppoint)
    point := *(*Point)(ppoint)
    println(point.x, point.y)
}

edited Oct 13, 2016 at 8:01

answered Oct 13, 2016 at 7:15

Mohanson

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2 Comments

Mohanson Over a year ago

In fact, I suggest use json string between C and Golang.

user3218590 Over a year ago

converting all different data types to json string before sending to Golang will take additional transformation logic what I was trying to avoid.

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