CGO中的C NULL类型

Question

I have a C function that returns NULL when an exception occurs. How can I check whether the returned value is NULL or not in Go since it has no built-in types to represent C NULL. Below is my code

retVal := C.myfunc()

if retVal == nil {
  // handle the error
}

Answer 1

I think you can use nil to test if the c function returns NULL. Try the following code:

package main

/*
#include <stdio.h>
#include <stdlib.h>

int* cfunc(int i) {
    if (i == 0) {
        return NULL;
    }

    int *p = (int*)malloc(sizeof(int));
    *p = 100;
    return p;
}
*/
import "C"

import "fmt"
import "unsafe"

func call_cfunc(i int32) {
    ret := C.cfunc(C.int(i))
    if ret == nil {
        fmt.Println("nil")
    } else {
        fmt.Println(*ret)
        C.free(unsafe.Pointer(ret))
    }
}

func main() {
    call_cfunc(0)
    call_cfunc(1)
}