用C语言求一个整数的幂的最有效方法是什么?

// 2^3
pow(2,3) == 8

// 5^5
pow(5,5) == 3125

PowerShell 1.0可以创建类似Unix的硬链接和软链接吗?

如果这不是内置的，有人能告诉我一个网站，有一个ps1脚本模仿这个吗?

恕我直言，这是任何优秀shell的必要功能。：）

我试图弄清楚如何使用boto3进行正确的错误处理。

我正在尝试创建一个IAM用户:

def create_user(username, iam_conn):
    try:
        user = iam_conn.create_user(UserName=username)
        return user
    except Exception as e:
        return e

当调用create_user成功时，我得到一个整洁的对象，其中包含API调用的http状态代码和新创建用户的数据。

例子:

{'ResponseMetadata': 
      {'HTTPStatusCode': 200, 
       'RequestId': 'omitted'
      },
 u'User': {u'Arn': 'arn:aws:iam::omitted:user/omitted',
           u'CreateDate': datetime.datetime(2015, 10, 11, 17, 13, 5, 882000, tzinfo=tzutc()),
           u'Path': '/',
           u'UserId': 'omitted',
           u'UserName': 'omitted'
          }
}

这很有效。但是当这个失败时(比如如果用户已经存在)，我只得到一个botocore.exceptions.ClientError类型的对象，其中只有文本告诉我哪里出错了。

例子: ClientError('调用CreateUser操作时发生错误(EntityAlreadyExists):省略名称的用户已经存在。')

这(AFAIK)使得错误处理非常困难，因为我不能只是打开结果的http状态代码(409用户已经存在根据AWS API文档的IAM)。这让我觉得我一定是做错了什么。最优的方法是boto3永远不抛出异常，但juts总是返回一个反映API调用如何进行的对象。

有没有人能在这个问题上给我一些启发，或者给我指出正确的方向?

给定函数foo:

fun foo(m: String, bar: (m: String) -> Unit) {
    bar(m)
}

我们可以:

foo("a message", { println("this is a message: $it") } )
//or 
foo("a message")  { println("this is a message: $it") }

现在，假设我们有以下函数:

fun buz(m: String) {
   println("another message: $m")
}

是否有一种方法，我可以通过“buz”作为参数“foo”? 喜欢的东西:

foo("a message", buz)

是否有一种简单的方法让Git总是为每次创建的提交或标记签名?

我尝试过这样的东西:

alias commit = commit -S

但这并没有奏效。

我不想安装一个不同的程序来实现这一点。这是容易做到的吗?

只是一个附带的问题，也许提交不应该被签名，只有标签，我从来没有创建，因为我提交单个提交的项目，如Homebrew等。

我想将NumPy数组转换为单位向量。更具体地说，我正在寻找这个归一化函数的等效版本:

def normalize(v):
    norm = np.linalg.norm(v)
    if norm == 0: 
       return v
    return v / norm

这个函数处理向量v的范数为0的情况。

在sklearn或numpy中是否提供了类似的函数?

我一直在阅读其他关于在Android应用程序中获得SIGSEGV的原因的帖子。我计划在我的应用程序中寻找可能与画布使用相关的空指针，但我的SIGSEGV每次都会抛出不同的内存地址。加上code=1和code=2。如果内存地址是0x00000000，我有一个线索，它是一个空指针。

我得到的最后一个是代码=2:

A/libc(4969): Fatal signal 11 (SIGSEGV) at 0x42a637d9 (code=2)

有什么建议吗?

I have a suspect, but I'm not keen on experimenting with it yet. My app uses the OSMDroid API for offline mapping. The OverlayItem class represents markers/nodes on the map. I have a Service that collects data via the network to populate the OverlayItem which are then displayed on the map. In an effort to simplify my design, I extended OverlayItem into my own NodeOverlayItem class, which includes some addition attributes I use in the UI Activity and in the Service. This gave me a single point of Item information for the UI and Service. I used Intents to broadcast to the Activity to refresh the UI map when something changed. The Activity binds to the Service and there's a Service method to get the list of NodeOverlayItem's. I think it might be the OSMDroid API's use of OverlayItem, and my Service updating node information at the same time. (a concurrency issue)

As I write this I think that's really the problem. The headache isn't splitting out the Node and OverlayItem from NodeOverlayItem, it's that the Activity will need some data from the Node, that the Service holds. Plus when the Activity is created (onResume, etc...) the OverlayItem objects will need to be re-created from the Node data that the Service has been maintaining while the Activity was away. e.g. You start the app, the Service collects data, the UI displays it, you go to Home, then back to the app, the Activity will need to pull and re-create the OverlayItem's from the latest Service node data.

我知道这不是一个很好的问题。就好像我所有的SO问题都是小众或模糊的。如果有人对如何解释这些SIGSEGV错误有建议，将不胜感激!

更新 下面是在调试会话期间捕获的最新崩溃。我有3个这样的设备用于测试，当我在开发和测试时，它们都不会可靠地崩溃。我额外添加了一些内容，以便能够注意到GC日志记录。您可以看到，这个问题可能与内存耗尽无关。

03-03 02:02:38.328: I/CommService(7477): Received packet from: 192.168.1.102
03-03 02:02:38.328: I/CommService(7477): Already processed this packet. It's a re-broadcast from another node, or from myself. It's not a repeat broadcast though.
03-03 02:02:38.406: D/CommService(7477): Checking OLSRd info...
03-03 02:02:38.460: D/CommService(7477): Monitoring nodes...
03-03 02:02:38.515: D/dalvikvm(7477): GC_CONCURRENT freed 2050K, 16% free 17151K/20359K, paused 3ms+6ms
03-03 02:02:38.515: I/CommService(7477): Received packet from: 192.168.1.102
03-03 02:02:38.515: D/CommService(7477): Forwarding packet (4f68802cf10684a83ac4936ebb3c934d) along to other nodes.
03-03 02:02:38.609: I/CommService(7477): Received packet from: 192.168.1.100
03-03 02:02:38.609: D/CommService(7477): Forwarding packet (e4bc81e91ec92d06f83e03068f52ab4) along to other nodes.
03-03 02:02:38.609: D/CommService(7477): Already processed this packet: 4204a5b27745ffe5e4f8458e227044bf
03-03 02:02:38.609: A/libc(7477): Fatal signal 11 (SIGSEGV) at 0x68f52abc (code=1)
03-03 02:02:38.914: I/DEBUG(4008): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
03-03 02:02:38.914: I/DEBUG(4008): Build fingerprint: 'Lenovo/IdeaTab_A1107/A1107:4.0.4/MR1/eng.user.20120719.150703:user/release-keys'
03-03 02:02:38.914: I/DEBUG(4008): pid: 7477, tid: 7712  >>> com.test.testm <<<
03-03 02:02:38.914: I/DEBUG(4008): signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 68f52abc
03-03 02:02:38.914: I/DEBUG(4008):  r0 68f52ab4  r1 412ef268  r2 4d9c3bf4  r3 412ef268
03-03 02:02:38.914: I/DEBUG(4008):  r4 001ad8f8  r5 4d9c3bf4  r6 412ef268  r7 4c479df8
03-03 02:02:38.914: I/DEBUG(4008):  r8 4d9c3c0c  r9 4c479dec  10 46cf260a  fp 4d9c3c24
03-03 02:02:38.914: I/DEBUG(4008):  ip 40262a04  sp 4d9c3bc8  lr 402d01dd  pc 402d0182  cpsr 00000030
03-03 02:02:38.914: I/DEBUG(4008):  d0  00000001000c0102  d1  3a22364574614c7d
03-03 02:02:38.914: I/DEBUG(4008):  d2  403fc0000000007d  d3  363737343433350a
03-03 02:02:38.914: I/DEBUG(4008):  d4  49544341223a2273  d5  6f6567222c224556
03-03 02:02:38.914: I/DEBUG(4008):  d6  3a223645676e6f4c  d7  000000013835372d
03-03 02:02:38.914: I/DEBUG(4008):  d8  0000000000000000  d9  4040000000000000
03-03 02:02:38.914: I/DEBUG(4008):  d10 0000000000000000  d11 4040000000000000
03-03 02:02:38.914: I/DEBUG(4008):  d12 4040000000000000  d13 0000000000000021
03-03 02:02:38.914: I/DEBUG(4008):  d14 0000000000000000  d15 0000000000000000
03-03 02:02:38.914: I/DEBUG(4008):  d16 3fe62e42fefa39ef  d17 3ff0000000000000
03-03 02:02:38.914: I/DEBUG(4008):  d18 3fe62e42fee00000  d19 0000000000000000
03-03 02:02:38.914: I/DEBUG(4008):  d20 0000000000000000  d21 3ff0000000000000
03-03 02:02:38.914: I/DEBUG(4008):  d22 4028000000000000  d23 3ff0000000000000
03-03 02:02:38.914: I/DEBUG(4008):  d24 0000000000000000  d25 3ff0000000000000
03-03 02:02:38.914: I/DEBUG(4008):  d26 0000000000000000  d27 c028000000000000
03-03 02:02:38.914: I/DEBUG(4008):  d28 0000000000000000  d29 3ff0000000000000
03-03 02:02:38.914: I/DEBUG(4008):  d30 3ff0000000000000  d31 3fecccccb5c28f6e
03-03 02:02:38.914: I/DEBUG(4008):  scr 60000013
03-03 02:02:39.046: I/DEBUG(4008):          #00  pc 0006b182  /system/lib/libcrypto.so (EVP_DigestFinal_ex)
03-03 02:02:39.046: I/DEBUG(4008):          #01  pc 0006b1d8  /system/lib/libcrypto.so (EVP_DigestFinal)
03-03 02:02:39.054: I/DEBUG(4008):          #02  pc 0001f814  /system/lib/libnativehelper.so
03-03 02:02:39.054: I/DEBUG(4008):          #03  pc 0001ec30  /system/lib/libdvm.so (dvmPlatformInvoke)
03-03 02:02:39.054: I/DEBUG(4008):          #04  pc 00058c70  /system/lib/libdvm.so (_Z16dvmCallJNIMethodPKjP6JValuePK6MethodP6Thread)
03-03 02:02:39.054: I/DEBUG(4008): code around pc:
03-03 02:02:39.054: I/DEBUG(4008): 402d0160 0003151e 4604b570 f7ff460d 4620ff81  ....p..F.F.... F
03-03 02:02:39.054: I/DEBUG(4008): 402d0170 f7ff4629 bd70ff93 4604b570 460e6800  )F....p.p..F.h.F
03-03 02:02:39.054: I/DEBUG(4008): 402d0180 68834615 dd062b40 21fa4810 44784a10  .F.h@+...H.!.JxD
03-03 02:02:39.054: I/DEBUG(4008): 402d0190 f7c8447a 6821f80f 698a4620 47904631  zD....!h F.i1F.G
03-03 02:02:39.054: I/DEBUG(4008): 402d01a0 b1154606 68836820 6822602b b12b6a13  .F.. h.h+`"h.j+.
03-03 02:02:39.054: I/DEBUG(4008): code around lr:
03-03 02:02:39.054: I/DEBUG(4008): 402d01bc 68e06821 21006c4a ea0af7c4 bd704630  !h.hJl.!....0Fp.
03-03 02:02:39.054: I/DEBUG(4008): 402d01cc 00031492 000314b5 4604b570 ffcef7ff  ........p..F....
03-03 02:02:39.054: I/DEBUG(4008): 402d01dc 46204605 ff12f7ff bd704628 4604b573  .F F....(Fp.s..F
03-03 02:02:39.054: I/DEBUG(4008): 402d01ec 2102460d fb36f002 42ab6823 b123d020  .F.!..6.#h.B .#.
03-03 02:02:39.054: I/DEBUG(4008): 402d01fc b1136c5b f7c868e0 68a0fccf 05c26025  [l...h.....h%`..
03-03 02:02:39.054: I/DEBUG(4008): memory map around addr 68f52abc:
03-03 02:02:39.054: I/DEBUG(4008): 4d8c5000-4d9c4000 
03-03 02:02:39.054: I/DEBUG(4008): (no map for address)
03-03 02:02:39.054: I/DEBUG(4008): b0001000-b0009000 /system/bin/linker
03-03 02:02:39.054: I/DEBUG(4008): stack:
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3b88  408d1f90  /system/lib/libdvm.so
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3b8c  412ef258  /dev/ashmem/dalvik-heap (deleted)
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3b90  00000001  
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3b94  408d6c58  /system/lib/libdvm.so
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3b98  408d6fa8  /system/lib/libdvm.so
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3b9c  4c479dec  
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3ba0  46cf260a  /system/framework/core.odex
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3ba4  408735e7  /system/lib/libdvm.so
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3ba8  412ef258  /dev/ashmem/dalvik-heap (deleted)
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3bac  002bf070  [heap]
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3bb0  412ef258  /dev/ashmem/dalvik-heap (deleted)
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3bb4  00000000  
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3bb8  412ef268  /dev/ashmem/dalvik-heap (deleted)
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3bbc  00000000  
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3bc0  df0027ad  
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3bc4  00000000  
03-03 02:02:39.054: I/DEBUG(4008): #00 4d9c3bc8  001ad8f8  [heap]
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3bcc  002ae0b8  [heap]
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3bd0  00000004  
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3bd4  402d01dd  /system/lib/libcrypto.so
03-03 02:02:39.054: I/DEBUG(4008): #01 4d9c3bd8  001ad8f8  [heap]
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3bdc  002ae0b8  [heap]
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3be0  00000004  
03-03 02:02:39.054: I/DEBUG(4008):     4d9c3be4  4024e817  /system/lib/libnativehelper.so
03-03 02:02:39.406: D/CommService(7477): Checking OLSRd info...
03-03 02:02:39.500: D/CommService(7477): Monitoring nodes...
03-03 02:02:39.500: D/dalvikvm(7477): GC_FOR_ALLOC freed 2073K, 16% free 17118K/20359K, paused 51ms
03-03 02:02:39.632: D/dalvikvm(7477): GC_CONCURRENT freed 1998K, 16% free 17162K/20359K, paused 2ms+4ms
03-03 02:02:40.406: D/CommService(7477): Checking OLSRd info...
03-03 02:02:40.445: D/CommService(7477): Monitoring nodes...
03-03 02:02:40.562: D/dalvikvm(7477): GC_CONCURRENT freed 2045K, 16% free 17158K/20359K, paused 3ms+4ms
03-03 02:02:41.406: D/CommService(7477): Checking OLSRd info...
03-03 02:02:41.445: D/CommService(7477): Monitoring nodes...
03-03 02:02:41.531: D/dalvikvm(7477): GC_CONCURRENT freed 2045K, 16% free 17154K/20359K, paused 3ms+12ms
03-03 02:02:42.406: D/CommService(7477): Checking OLSRd info...
03-03 02:02:42.445: D/CommService(7477): Monitoring nodes...
03-03 02:02:42.507: D/dalvikvm(7477): GC_CONCURRENT freed 2068K, 16% free 17128K/20359K, paused 3ms+4ms
03-03 02:02:42.679: D/dalvikvm(7477): GC_CONCURRENT freed 2006K, 16% free 17161K/20359K, paused 2ms+12ms
03-03 02:02:43.140: I/BootReceiver(1236): Copying /data/tombstones/tombstone_05 to DropBox (SYSTEM_TOMBSTONE)
03-03 02:02:43.210: D/dalvikvm(1236): GC_FOR_ALLOC freed 912K, 17% free 10207K/12295K, paused 62ms
03-03 02:02:43.265: D/dalvikvm(1236): GC_FOR_ALLOC freed 243K, 16% free 10374K/12295K, paused 49ms
03-03 02:02:43.265: I/dalvikvm-heap(1236): Grow heap (frag case) to 10.507MB for 196628-byte allocation

在PowerShell中是否有一种简单的方法来计时命令的执行，就像Linux中的'time'命令一样? 我想到了这个:

$s=Get-Date; .\do_something.ps1 ; $e=Get-Date; ($e - $s).TotalSeconds

但我想要简单点的，比如

time .\do_something.ps1

现在，我已经在matlab, fortran中遇到过几次这个术语…其他的…但我从来没有找到一个解释，它是什么意思，它是什么?所以我在这里问，什么是向量化，例如，“一个循环是向量化的”是什么意思?

我有一个boto3客户端:

boto3.client('kms')

但这发生在新机器上，它们动态地打开和关闭。

    if endpoint is None:
        if region_name is None:
            # Raise a more specific error message that will give
            # better guidance to the user what needs to happen.
            raise NoRegionError()

为什么会这样?为什么只是部分时间?