从 go 调用 C 函数

Question

我对学习 go 语言很陌生，我开始成为这个语言的 super 爱好者语。我希望，我很快就会成为一名优秀的地鼠。目前我尝试调用 C 函数读取影子文件，我的代码是:

// #cgo CFLAGS: -D_POSIX_SOURCE=1
// #include <stdlib.h>
// #include <shadow.h>
// size_t size_of_shadow() { return sizeof(struct spwd); }
import "C"
import "unsafe"
import "fmt"

type Shadow struct {
    Name   string
    Passwd string
}

func Getspnam(name string) (*Shadow, error) {
    cname := C.CString(name)
    cspwd := (*C.struct_passwd)(C.malloc(C.size_of_shadow()))
    buf := (*C.char)(C.malloc(1024))
    _, err := C.getspnam_r(cname, cspwd, 1024, &cpwd)

    if unsafe.Pointer(cspwd) == unsafe.Pointer(uintptr(0)) {
        C.free(unsafe.Pointer(cname))

        if err == nil {
            err = fmt.Errorf("User %s not found", name)
        }

        return nil, err
    }

    s := Shadow{
        Name: C.GoString(cspwd.sp_namp),
        Passwd: C.GoString(cspwd.sp_pwdp),
    }

    C.free(unsafe.Pointer(cname))
    C.free(unsafe.Pointer(cspwd))
    C.free(unsafe.Pointer(buf))

    return &s, nil
}

受这个小项目和函数文档的启发类(class):

https://github.com/LTD-Beget/passwd http://linux.die.net/man/3/getspnam

我正在使用 debian stretch and go 1.6 版本，与包管理器一起安装。当我尝试编译我的文件时出现错误:

could not determine kind of name for C.getspnam_r

但是当我打开头文件 shadow.h 时，该函数却存在于文件。

Answer 1

我改正了我的错误。错误是使用了一些不必要的标志以及结构名称上的拼写错误:

// #include <stdlib.h>
// #include <shadow.h>
// size_t size_of_shadow() { return sizeof(struct spwd); }
import "C"

import "C"
import "unsafe"
import "fmt"

type Shadow struct {
    Name   string
    Passwd string
}

func Getspnam(name string) (*Shadow, error) {
    cname := C.CString(name)
    defer C.free(unsafe.Pointer(cname))

    cspwd := (*C.struct_spwd)(C.malloc(C.size_of_shadow()))
    defer C.free(unsafe.Pointer(cspwd))

    buf := (*C.char)(C.malloc(1024))
    defer C.free(unsafe.Pointer(buf))

    _, err := C.getspnam_r(cname, cspwd, buf, 1024, &cspwd)

    if unsafe.Pointer(cspwd) == unsafe.Pointer(uintptr(0)) {
        if err == nil {
            err = fmt.Errorf("User %s not found", name)
        }

        return nil, err
    }

    s := Shadow{
        Name:   C.GoString(cspwd.sp_namp),
        Passwd: C.GoString(cspwd.sp_pwdp),
    }

    return &s, nil
}

新版本的代码。