Caution
Because assigning an array to another variable resets the original array’s pointer,our example above would cause an endless loop had we assigned $fruit to another variable inside the loop.

一个例子：

<?PHP
$fruit = array('a' => 'apple','b' => 'banana','c' => 'cranBerry');

reset($fruit);
while (list($key,$val) = each($fruit)) {
    echo "$key => $val\n";
}
?>

好的.这说得通.但我决定做一个简单的测试：

<?PHP
    $fruit = array('a' => 'apple','c' => 'cranBerry');

    foreach ($fruit as $key => $name) {
        printf("[%s] => [%s]\n",$key,$name);
    }

    $fruit2 = $fruit;
    echo current($fruit);
?>

结果是预期的：指针已被重置.我的问题是指针是否仅在数组结束后重置？

例如：

<?PHP
    $fruit = array('a' => 'apple',$name);
    }

    reset($fruit);
    next($fruit)."\n";
    $fruit2 = $fruit;
    echo current($fruit);
?>

指针保留在第二个数组元素中(‘b’=>’banana’).
这种行为是语言的特征吗？

谢谢你,对不起英语不好意思.

This behavior is characteristic of language?

PHP数组中“指针”的含义与“指针”的一般含义不同(在C/C++或其他语言中,程序员可以直接访问内存).

PHP中没有指针. array数据类型将光标内部保留在其包含的值列表中.它被称为数组的内部指针,它由函数reset(),next(),prev(),end(),each()以及其他函数修改.它可以用于迭代数组,如下所示：

$array = array(1,2,3);
while (list($key,$val) = each($array)) {
    echo($key.' => '.$val."\n");
}

没有可靠的方法来使用next()或prev()迭代数组,因为当没有更多元素要迭代时它们返回FALSE但是当值FALSE作为元素存储在数组中时它们也返回FALSE.

如果您只需要从数组的开头(或结尾)分析几个项目,它们可能很有用. F.E.假设我们有一个由函数返回的整数数组,我们需要得到第一个不为零的值.

但使用foreach()可以更轻松地实现这一目标：

$array = array(0,1,3);
foreach ($array as $val) {
    if ($val != 0) {
        break;
    }
}
echo($val);           // prints "2"

或array_shift()：

$array = array(0,3);
do {
    $val = array_shift($array);
    if ($val != 0) {
        break;
    }
} while(count($array));
echo($val);           // prints "2"

The result is expected: the pointer has been reset. My question is if the pointer is reset only after the end of the array?

foreach()的文档是错误的.也许它在PHP 3和PHP 4上是正确的,但我认为自从PHP 5中引入iterators以来,foreach()的行为发生了变化(更好).

它说：

When foreach first starts executing,the internal array pointer is automatically reset to the first element of the array. This means that you do not need to call reset() before a foreach loop.

As foreach relies on the internal array pointer,changing it within the loop may lead to unexpected behavior.

一个简单的测试与此陈述相矛盾：

$array = array(1,3,5,7,9);

foreach ($array as $val1) {
    foreach ($array as $val2) {
        echo('$val1='.$val1.'; $val2='.$val2.'; ');
    }
    echo("\n");
}

它没有问题.如果foreach()使用内部数组指针,它应该不起作用.它可能会创建指针的副本.

您还可以尝试在foreach()中使用current(),next(),prev()或reset(),您将获得令人惊讶且有时不一致的结果.

最好使用foreach()迭代数组,不要以任何方式依赖内部指针.

但是,当您需要获取数组的第一个和最后一个元素而不必担心键时,函数reset()和end()非常方便.

int myData(uint myHandle,tchar *dataname,long *Time,uint *maxData,DATASTRUCT **data);

typedef struct {
  byte Rel;
  __int64 Time;
  char Validated;
  unsigned char Data[1];
} DATASTRUCT ;

我的C#声明如下：

[DllImport("myData.dll",EntryPoint = "myData")]
public static extern int myData(uint myHandle,[MarshalAs(UnmanagedType.LPTStr)] string dataname,out long Time,out uint maxData,ref DATASTRUCT[] data);

[StructLayout(LayoutKind.Sequential,Pack = 1)]
public struct DATASTRUCT
{
    public sbyte Rel;
    public long Time;
    public byte Validated;
    public double Data;
}

然后我调用托管函数如下：

string dataToShow = "description";
long Time;
uint maxData; // How many structs will be returned,i.e. how much data is available
uint myHandle = 1;

DATASTRUCT[] datainformation = new DATASTRUCT[3]; // doesn't matter what I specify as the array size?

myData(myHandle,dataToShow,out Time,out maxData,ref datainformation);

在执行时,即使有3个返回,上述函数也将成功返回只有一个结构.为什么会这样？

附加信息;我试过通过以下方式将指针传递给结构数组的指针：

- ref DATASTRUCT[] data; // Works but only returns one struct
- [Out,MarshalAs(UnmanagedType.LPArray)] DATASTRUCT[] data; // returns the number of defined structs with garbage

据我了解,我可能需要使用IntPtr进行一些手动编组,但我不知道如何实现这一点,所以任何建议都将受到赞赏.

将您的API定义更改为(注意,我将maxData参数更改为uint,.NET中为64位,本机为32位).

[DllImportAttribute("myData.dll",out uint Time,out IntPtr pData);

我不记得你是否需要最后一个参数的out关键字,但我想是的.

然后,调用myData：

uint nAllocs = 0,time = 0;
IntPtr pAllocs = IntPtr.Zero;
myData(1,"description",out time,out nAllocs,out pAllocs);

现在,pAllocs应该指向非托管内存,将这些内容编组到托管内存中并不太难：

[StructLayoutAttribute(LayoutKind.Sequential,Pack = 1)]
public struct DATASTRUCT
{
    public byte Rel;
    public long Time;
    public byte Validated;
    public IntPtr Data; //pointer to unmanaged string.
}


int szStruct = Marshal.SizeOf(typeof(DATASTRUCT));
DATASTRUCT[] localStructs = new DATASTRUCT[nAllocs];
for(uint i = 0; i < nallocs; i++)
    localStructs[i] = (DATASTRUCT)Marshal.PtrToStructure(new IntPtr(pAllocs.ToInt32() + (szStruct * i)),typeof(DATASTRUCT));

现在你应该有一系列本地结构.

需要注意的一点您可能需要将项目设置为编译为x86,以将IntPtr的大小标准化为4字节(DWORD)而不是Anycpu的默认值8.

*p = p[0];
    (*p)[1]  == array[1];
    p[0][1]  == (*p)[1] == array[1];