[英]How to pinvoke a variable-length array of structs from GetTokenInformation() safely for 32-bit and 64-bit? C#
[英]C# pInvoke with long in both 32 & 64 Bit Linux:
我需要調用Linux函數sysinfo
它的聲明是int sysinfo(struct sysinfo * info); 同
在Linux 2.3.16之前,sysinfo()用於以以下結構返回信息:
struct sysinfo {
long uptime; /* Seconds since boot */
unsigned long loads[3]; /* 1, 5, and 15 minute load averages */
unsigned long totalram; /* Total usable main memory size */
unsigned long freeram; /* Available memory size */
unsigned long sharedram; /* Amount of shared memory */
unsigned long bufferram; /* Memory used by buffers */
unsigned long totalswap; /* Total swap space size */
unsigned long freeswap; /* swap space still available */
unsigned short procs; /* Number of current processes */
char _f[22]; /* Pads structure to 64 bytes */
};
大小以字節為單位。
從Linux 2.3.23(i386),2.3.48(所有體系結構)開始,結構為:
struct sysinfo {
long uptime; /* Seconds since boot */
unsigned long loads[3]; /* 1, 5, and 15 minute load averages */
unsigned long totalram; /* Total usable main memory size */
unsigned long freeram; /* Available memory size */
unsigned long sharedram; /* Amount of shared memory */
unsigned long bufferram; /* Memory used by buffers */
unsigned long totalswap; /* Total swap space size */
unsigned long freeswap; /* swap space still available */
unsigned short procs; /* Number of current processes */
unsigned long totalhigh; /* Total high memory size */
unsigned long freehigh; /* Available high memory size */
unsigned int mem_unit; /* Memory unit size in bytes */
char _f[20-2*sizeof(long)-sizeof(int)]; /* Padding to 64 bytes */
};
這是我到目前為止的內容:
該功能pinvoke:
private const string DoesntFindLibC =@"/lib/x86_64-linux-gnu/libc.so.6";
[System.Runtime.InteropServices.DllImport(DoesntFindLibC)]
private static extern int sysinfo(ref sysinfo_t info);
和結構映射:
[System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
struct sysinfo_t
{
public System.UIntPtr uptime; /* Seconds since boot */
[System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst=3)]
public System.UIntPtr [] loads; /* 1, 5, and 15 minute load averages */
public System.UIntPtr totalram; /* Total usable main memory size */
public System.UIntPtr freeram; /* Available memory size */
public System.UIntPtr sharedram; /* Amount of shared memory */
public System.UIntPtr bufferram; /* Memory used by buffers */
// [System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.
public System.UIntPtr totalswap; /* Total swap space size */
public System.UIntPtr freeswap; /* swap space still available */
public ushort procs; /* Number of current processes */
[System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst=22)]
public char[] _f; /* Pads structure to 64 bytes */
}
問題在於,C代碼中的“ long”是特定於處理器體系結構的,因為在x86 32位Linux中,long的大小是32位,在x86 64位Linux中是64位,所以我必須選擇IntPtr,並且因為它是未簽名的,所以我選擇了UIntPtr。
但是,在C#/ mono中,long始終定義為Int64。
現在使用IntPtr有點不方便。 有什么我可以應用的MarshalAs屬性,或者我可以編寫一個自定義的marshaler以便我實際上可以在結構中包含ulong,但是它本地映射到IntPtr嗎? 這樣,相同的代碼就可以在x86-32和x86-64上運行。
不,您無法采取任何編組魔術來解決此問題。
但是,您可以隱藏字段並提供屬性訪問器:
using System.Runtime.InteropServices;
[StructLayoutAttribute(LayoutKind.Sequential)]
struct sysinfo_t
{
System.UIntPtr _uptime; /* Seconds since boot */
public ulong uptime {
get { return (ulong) _uptime; }
set { _uptime = new UIntPtr (value); }
}
[MarshalAs(UnmanagedType.ByValArray, SizeConst=3)]
System.UIntPtr [] _loads; /* 1, 5, and 15 minute load averages */
public ulong[] loads {
get { return new ulong [] { (ulong) _loads [0], (ulong) _loads [1], (ulong) _loads [1]) };
set { _loads = new UIntPtr [] { new UIntPtr (value [0]), new UIntPtr (value [1]), new UIntPtr (value [2]) }; }
}
// etc
}
C'long'類型很難封送,因為.NET中沒有在所有平台上都與其大小匹配的類型。 問題在於,在某些平台(Win32,Win64和Linux32)上,C'long'類型的長度可以為4個字節,而在其他平台(Linux64)上,其長度可以為8個字節。 在.NET中,不管平台如何,都有“ int”類型,它的長度為4個字節,而與平台無關,則是“ long”類型,它的長度為8個字節。 它們都不能用作C'long'類型的多平台替代方案,並且單據文檔建議使用IntPtr,因為您已經發現了,但是我發現這種方法非常不方便(在Win64上也無法使用!)。 因此,我個人更喜歡封送兩組不同的函數和結構 ,對於C'long'類型為4字節長的平台,其一組為 'int'.NET類型,對於C為'long'的平台,其另一組為'long'.NET類型。 '類型為8個字節長。 然后,我只在運行時使用if (IntPtr.Size == 8)
條件來決定應使用哪個集合。
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