从C到Golang获取结构

Question

c.h

typedef signed int VarInt32;

typedef struct {
    VarInt32   VI32
} VAR_A, *VAR_B

int Add(VAR_B v_b) //the argument is a pointer

var mvar unsafe.Pointer

C.Add((*C.VAR_B)(&mvar))

fmt.Println(mvar)

得到这样的结果:

warning: passing argument 1 of ‘add’ from incompatible pointer type [enabled by default]
note: expected ‘MVAR’ but argument is of type ‘struct <anonymous> *’

这似乎不正确，

我正在golang寻找类似的东西：mvar.VI32

谢谢

我的头很痛，不擅长C / C，

这是我的场景，调用一个SDK（带有.so库）

c.h

typedef char*   MPChar;
typedef MLong   MRESULT;

typedef struct{
    MPChar startTime;       
    MPChar endTime;         
    MPChar platform;        
    MPChar sdkType;         
    MPChar appId;           
    MPChar sdkKey;          
    MPChar sdkVersion;      
    MPChar fileVersion;     
}ASF_ActiveFileInfo, *LPASF_ActiveFileInfo;


MRESULT ASFGetActiveFileInfo(
    LPASF_ActiveFileInfo  activeFileInfo 
);

我试着用Go语言调用函数ASFGetActiveFileInfo，如下所示：

var c_afInfo C.ASF_ActiveFileInfo

C.ASFGetActiveFileInfo(&c_afInfo)

//get the same error
//C.ASFGetActiveFileInfo((C.LPASF_ActiveFileInfo)(unsafe.Pointer(&c_afInfo)))

得到这个错误：

# command-line-arguments
cgo-gcc-prolog: In function ‘_cgo_8c613494cf5f_Cfunc_ASFGetActiveFileInfo’:
cgo-gcc-prolog:52:2: warning: passing argument 1 of ‘ASFGetActiveFileInfo’ from incompatible pointer type [enabled by default]
In file included from ./main.go:7:0:
./inc/arcsoft_face_sdk.h:104:9: note: expected ‘LPASF_ActiveFileInfo’ but argument is of type ‘struct <anonymous> *’
 MRESULT ASFGetActiveFileInfo(
         ^
# command-line-arguments
./main.go:134:139: cannot use _cgo0 (type *_Ctype_LPASF_ActiveFileInfo) as type *_Ctype_struct___0 in argument to _Cfunc_ASFGetActiveFileInfo

尝试：

var c_afInfo C.LPASF_ActiveFileInfo

C.ASFGetActiveFileInfo((C.LPASF_ActiveFileInfo)&c_afInfo)

得到这个错误

# command-line-arguments
cgo-gcc-prolog: In function ‘_cgo_061c0167bf6c_Cfunc_ASFGetActiveFileInfo’:
cgo-gcc-prolog:52:2: warning: passing argument 1 of ‘ASFGetActiveFileInfo’ from incompatible pointer type [enabled by default]
In file included from ./main.go:7:0:
./inc/arcsoft_face_sdk.h:104:9: note: expected ‘LPASF_ActiveFileInfo’ but argument is of type ‘struct <anonymous> *’
 MRESULT ASFGetActiveFileInfo(
         ^
# command-line-arguments
./main.go:134:25: type _Ctype_LPASF_ActiveFileInfo is not an expression

这个问题有什么解决方案吗？

感谢@peterSO的回答，它工作，但仍然显示错误：

cgo-gcc-prolog: In function ‘_cgo_73061f0a5639_Cfunc_ASFGetActiveFileInfo’:
cgo-gcc-prolog:98:2: warning: passing argument 1 of ‘ASFGetActiveFileInfo’ from incompatible pointer type [enabled by default]
In file included from ./main.go:7:0:
./inc/arcsoft_face_sdk.h:104:9: note: expected ‘LPASF_ActiveFileInfo’ but argument is of type ‘struct <anonymous> *’
 MRESULT ASFGetActiveFileInfo(
         ^
0 linux

事实非常接近

演示：https://github.com/JoeZing/stackdemo

Answer 1

围棋与 cgo 中所有晦涩难懂的 C 类型划分规则都不匹配。保持简单。

使用no struct标记示例，以下是一些将C struct变量和指针参数从Go传递到C Add函数的方法。它是不安全的，绕过了Go和C (GCC C编译器)检查。

package main

/*
// GNU Compiler Collection (GCC): Warning Options
// https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#Warning-Options
#cgo CFLAGS: -Wno-incompatible-pointer-types

typedef signed int i32_t;

// anonymous (no tag) struct
typedef struct {
    i32_t i;
} sv_t, *sp_t;

int Add(sv_t v, sp_t p);

int Add(sv_t v, sp_t p) {
    int sum = v.i;
    if (p) {
        sum += p->i;
    }
    return sum;
}
*/
import "C"

import (
    "fmt"
    "unsafe"
)

func main() {
    var svar C.sv_t
    svar.i = 42
    fmt.Printf("svar: %v  svar.i: %v\n", svar, svar.i)

    var sptr C.sp_t
    sptr = (C.sp_t)(unsafe.Pointer(new(C.sv_t)))
    sptr.i = 39
    fmt.Printf("sptr: %v  sptr.i: %v\n", sptr, sptr.i)

    sum := C.Add(svar, sptr)
    fmt.Print("Add(", svar.i, ", ", sptr.i, ") = ", sum, "\n")

    fmt.Printf("svar: %T\nsptr: %T\n", svar, sptr)
}

/*

输出：

$ go run so.go
svar: {42}  svar.i: 42
sptr: &{39}  sptr.i: 39
Add(42, 39) = 81
svar: main._Ctype_struct___0
sptr: main._Ctype_sp_t
$ 

对于您的具体示例，也许是这样的：

package main

/*
// GNU Compiler Collection (GCC): Warning Options
// https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#Warning-Options
#cgo CFLAGS: -Wno-incompatible-pointer-types

typedef long    MLong;
typedef char*   MPChar;
typedef MLong   MRESULT;

typedef struct {
    MPChar startTime;
    MPChar endTime;
    MPChar platform;
    MPChar sdkType;
    MPChar appId;
    MPChar sdkKey;
    MPChar sdkVersion;
    MPChar fileVersion;
} ASF_ActiveFileInfo, *LPASF_ActiveFileInfo;


MRESULT ASFGetActiveFileInfo(
    LPASF_ActiveFileInfo  activeFileInfo
);

MRESULT ASFGetActiveFileInfo(
    LPASF_ActiveFileInfo  activeFileInfo
)
{
    activeFileInfo->appId = "Go";
    return 42;
}
*/
import "C"

import (
    "fmt"
    "unsafe"
)

func main() {
    asfPtr := (C.LPASF_ActiveFileInfo)(unsafe.Pointer(new(C.ASF_ActiveFileInfo)))
    r := C.ASFGetActiveFileInfo(asfPtr)
    fmt.Println(r, C.GoString(asfPtr.appId))
}

输出：

$ go run so.go
42 Go
$ 

使用您的示例（使用＜code＞struct

package main

/*
typedef signed int i32_t;

typedef struct s_t {
    i32_t i;
} sv_t, *sp_t;

int Add(sv_t v, sp_t p);

int Add(sv_t v, sp_t p) {
    int sum = v.i;
    if (p) {
        sum += p->i;
    }
    return sum;
}
*/
import "C"

import (
    "fmt"
    "unsafe"
)

func main() {
    svar := C.struct_s_t{i: 42}

    sptr := &C.struct_s_t{i: 39}
    sum := C.Add(svar, sptr)
    fmt.Print("Add(", svar.i, ", ", sptr.i, ") = ", sum, "\n")

    uptr := unsafe.Pointer(&C.struct_s_t{i: 7})
    sum = C.Add(svar, (C.sp_t)(uptr))
    fmt.Print("Add(", svar.i, ", ", (C.sp_t)(uptr).i, ") = ", sum, "\n")
    sum = C.Add(svar, (*C.struct_s_t)(uptr))
    fmt.Print("Add(", svar.i, ", ", (*C.struct_s_t)(uptr).i, ") = ", sum, "\n")

    fmt.Printf("svar: %T\nsptr: %T\nuptr: %T\n", svar, sptr, uptr)
}

输出：

$ go run so.go
Add(42, 39) = 81
Add(42, 7) = 49
Add(42, 7) = 49
svar: main._Ctype_struct_s_t
sptr: *main._Ctype_struct_s_t
uptr: unsafe.Pointer
$