pointers - 戈朗 Cgo : panic: runtime error: cgo argument has Go pointer to Go pointer

Question

我正在使用一个 C 库，与下面不同，我无法控制它。我需要将指向也包含指针的数组的指针传递给 C 函数。

package main

/*
#include <stdio.h>

typedef int* pInt;

void foo(pInt p[]) {
  printf("foo()\n");
}
*/
import "C"
import "unsafe"

func main() {
    var i C.int
    var p1 C.pInt = (*C.int)(unsafe.Pointer(&i))
    var p2 C.pInt = (*C.int)(unsafe.Pointer(&i))
    var ps []C.pInt = []C.pInt{p1, p2}
    C.foo(unsafe.Pointer(&ps[0]))
}

此代码导致错误 panic: runtime error: cgo argument has Go pointer to Go pointer。我想知道如何重写这段代码的 Go 部分，使其满足 Cgo 的指针规则。我希望我无需编写 C 帮助程序代码就可以做到这一点。

Answer 1

坏消息，你必须在 C 中定义你的助手。好消息，它只有 2 行。

package main

/*
#include <stdlib.h> // for malloc/free
#include <stdio.h>

typedef int* pInt;

void foo(pInt p[]) { // you probably wanna pass a len to the function.
    *p[0] = 100;
    printf("foo()\n");
}

pInt * allocArray(size_t ln) { return (pInt*) malloc(ln * sizeof(pInt)); }
void freeArr(pInt * p) { free(p); }

*/
import "C"
import "unsafe"

func main() {
    var (
        i, sz  = 0, 2
        arr    = C.allocArray(C.size_t(sz))
        ps     = (*[100000]C.pInt)(unsafe.Pointer(arr))[:sz:sz]
        p1, p2 = (C.pInt)(unsafe.Pointer(&i)), (C.pInt)(unsafe.Pointer(&i))
    )
    ps[0], ps[1] = p1, p2
    C.foo(arr)
    C.freeArr(arr)
    println("i", i)
}