如何在PowerShell中创建含普通数组的非托管结构体并正确赋值？

问题根源 #

1. 数组未初始化：.NET结构体中的引用类型（如数组）默认初始化为null，直接索引赋值会抛出"Cannot index into a null array"错误。
2. 类型不匹配：原代码中Int16/Int32与C结构体的uint16_t类型不对应，会导致内存布局偏差，必须改用UInt16匹配无符号16位整数。

修复数组初始化问题 #

先为thresholds数组分配指定大小的实例，再进行元素赋值：

$typeCode = @'
using System;
using System.Runtime.InteropServices;

[StructLayout(LayoutKind.Sequential, Pack = 1)]
[Serializable]
public struct MyConfig
{
    public UInt16 level; // 匹配C的uint16_t
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)] 
    public UInt16[] thresholds; // 匹配C的uint16_t[16]
}
'@

Add-Type -TypeDefinition $typeCode

$config = New-Object MyConfig
$config.level = 1

# 先初始化数组
$config.thresholds = New-Object UInt16[] 16
# 逐个赋值
$config.thresholds[0] = 1
$config.thresholds[1] = 2
# ... 其他元素按需赋值

将结构体序列化为二进制Blob并写入文件 #

使用System.Runtime.InteropServices.Marshal类完成结构体到字节数组的转换，再写入文件：

# 计算结构体大小
$structSize = [System.Runtime.InteropServices.Marshal]::SizeOf($config)
# 分配非托管内存
$ptr = [System.Runtime.InteropServices.Marshal]::AllocHGlobal($structSize)
try {
    # 将结构体拷贝到非托管内存
    [System.Runtime.InteropServices.Marshal]::StructureToPtr($config, $ptr, $false)
    # 从非托管内存读取字节数组
    $byteArray = New-Object byte[] $structSize
    [System.Runtime.InteropServices.Marshal]::Copy($ptr, $byteArray, 0, $structSize)
    # 写入文件
    [System.IO.File]::WriteAllBytes("MyConfig.bin", $byteArray)
}
finally {
    # 释放非托管内存，避免泄漏
    [System.Runtime.InteropServices.Marshal]::FreeHGlobal($ptr)
}

完整示例代码 #

$typeCode = @'
using System;
using System.Runtime.InteropServices;

[StructLayout(LayoutKind.Sequential, Pack = 1)]
[Serializable]
public struct MyConfig
{
    public UInt16 level;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)] 
    public UInt16[] thresholds;
}
'@

Add-Type -TypeDefinition $typeCode

# 初始化结构体
$config = New-Object MyConfig
$config.level = 1
$config.thresholds = New-Object UInt16[] 16

# 填充数组数据
for ($i = 0; $i -lt 16; $i++) {
    $config.thresholds[$i] = [UInt16]($i + 1)
}

# 序列化并写入文件
$structSize = [System.Runtime.InteropServices.Marshal]::SizeOf($config)
$ptr = [System.Runtime.InteropServices.Marshal]::AllocHGlobal($structSize)
try {
    [System.Runtime.InteropServices.Marshal]::StructureToPtr($config, $ptr, $false)
    $byteArray = New-Object byte[] $structSize
    [System.Runtime.InteropServices.Marshal]::Copy($ptr, $byteArray, 0, $structSize)
    [System.IO.File]::WriteAllBytes("MyConfig.bin", $byteArray)
    Write-Host "结构体已成功写入MyConfig.bin"
}
finally {
    [System.Runtime.InteropServices.Marshal]::FreeHGlobal($ptr)
}

内容的提问来源于stack exchange，提问作者Richard W