Question

我正在使用一个C库，与以下不同，我无法控制。我需要向C函数传递一个指向同样包含指针的数组的指针。

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]))
}

此代码会导致错误panic: runtime error: cgo argument has Go pointer to Go pointer。我想知道如何重写此代码的Go部分，以便它满足Cgo的指针规则。我希望无需编写C帮助程序代码即可完成此操作。

Answer 1

坏消息，您必须在C中定义帮助者。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)
}

Answer 2

在没有C帮助函数的情况下修改OneOfOne的解决方案，虽然很高兴看到C帮助函数在go文件的注释中写得多么容易。

package main

/*
#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");
}

*/
import "C"
import "unsafe"

func main() {
    var (
        i, sz  = 0, 2
        arr    = (*C.pInt)(C.malloc(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.free(unsafe.Pointer(arr))
    println("i", i)
}

Golang Cgo：恐慌：运行时错误：cgo参数有Go指针指向Go指针

2 个答案: