zero

What is the difference between null, 0 and nothing?

由 筅森魡賤 提交于 2019-12-10 12:55:37
问题 What is the difference between null , 0 and nothing ? I cannot find a question addressing all three of these. For example: If I am getting input from a string and parsing it to int . return Integer.parseInt(sc.nextLine()); Or if I am asking if a string != "" , or a is not nothing I am confused about which to use when and why. I am confused about which one to use when validating data. 回答1: null means that a variable contains a reference to a space in memory that does not contain an object. 0

How do I delete a row in a numpy array which contains a zero? [duplicate]

由 本秂侑毒 提交于 2019-12-10 03:34:10
问题 This question already has answers here : remove zero lines 2-D numpy array (3 answers) Closed 3 years ago . I'm trying to write a function to delete all rows in which have a zero value in. This is not from my code, but an example of the idea I am using: import numpy as np a=np.array(([7,1,2,8],[4,0,3,2],[5,8,3,6],[4,3,2,0])) b=[] for i in range(len(a)): for j in range (len(a[i])): if a[i][j]==0: b.append(i) print 'b=', b for zero_row in b: x=np.delete(a,zero_row, 0) print 'a=',a and this is

Oracle, adding leading zeros to string (not number)

由 Deadly 提交于 2019-12-09 05:14:23
问题 I am using Oracle (work space is TOAD) and I need to make my strings that if they are shorted then 10 characters then add leading zeros to make them all 10 digit strings. For example if I have a string like this: '12H89' need to be '0000012H89' or '1234' to be '0000001234' How can this be done? Whats the best way? Thanks in advance . 回答1: You can use the LPAD function for that, passing in the string, the length you want it to be, and the character to pad it with. For 10 digits with leading

Why is “0 === -0” true in JavaScript?

由 ε祈祈猫儿з 提交于 2019-12-08 19:10:33
问题 In a recent post on http://wtfjs.com/. An author writes following without explanation which happens to be true. 0 === -0 //returns true My understanding about === operator is it returns true if operands point to same object. Also, - operator returns a reference to negative value of operand. With this rule, 0 and -0 should not be the same. So, why is 0 === -0 ? 回答1: In fact, 0 and -0 are not the same even at the bit level. However, there is a special case implemented for +/-0 so they compare

Python Pandas Scientific Notation Iconsistent

由 爱⌒轻易说出口 提交于 2019-12-08 05:47:28
问题 I am looking into rewriting some data analysis code using Pandas (since I just discovered it) on Ubuntu 14.04 64-bit and I have hit upon some strange behaviour. My data files look like this: 26/09/2014 00:00:00 2.423009 -58.864655 3.312355E-7 6.257226E-8 302 305 26/09/2014 00:00:00 2.395637 -62.73302 3.321525E-7 7.065322E-8 302 305 26/09/2014 00:00:01 2.332541 -57.763269 3.285718E-7 6.873837E-8 302 305 26/09/2014 00:00:02 2.366828 -51.900812 3.262279E-7 7.397762E-8 302 305 26/09/2014 00:00:03

JAVA Zero Copy的相关知识

由 喜你入骨 提交于 2019-12-07 09:41:50
介绍 java 的zero copy多在网络应用程序中使用。Java的libaries在linux和unix中支持zero copy，关键的api是java.nio.channel.FileChannel的transferTo()，transferFrom()方法。我们可以用这两个方法来把bytes直接从调用它的channel传输到另一个writable byte channel，中间不会使data经过应用程序，以便提高数据转移的效率。 许多web应用都会向用户提供大量的静态内容，这意味着有很多data从硬盘读出之后，会原封不动的通过socket传输给用户。这种操作看起来可能不会怎么消耗CPU，但是实际上它是低效的：kernal把数据从disk读出来，然后把它传输给user级的application，然后application再次把同样的内容再传回给处于kernal级的socket。这种场景下，application实际上只是作为一种低效的中间介质，用来把disk file的data传给socket。 data每次穿过user-kernel boundary，都会被copy，这会消耗cpu，并且占用RAM的带宽。幸运的是，你可以用一种叫做Zero-Copy的技术来去掉这些无谓的 copy。应用程序用zero copy来请求kernel直接把disk的data传输给socket

Declare a 0-Length String Array in VBA - Impossible?

由 风格不统一 提交于 2019-12-07 04:46:42
问题 Is it really not possible to declare a 0-length array in VBA? If I try this: Dim lStringArr(-1) As String I get a compile error saying range has no values. If I try to trick the compiler and redim at runtime like this: ReDim lStringArr(-1) I get a subscript out of range error. I've varied the above around a bit but with no luck e.g. Dim lStringArr(0 To -1) As String Use Case I want to convert a variant array to a string array. The variant array may be empty as it comes from the Keys property

In C, is there a difference between a NULL pointer and a pointer that points to 0? If so, what?

由 佐手、 提交于 2019-12-07 04:17:03
问题 In C, what is the difference between a NULL pointer and a pointer that points to 0? 回答1: The ISO/IEC 9899:TC2 states in 6.3.2.3 Pointers 3 An integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant.55) If a null pointer constant is converted to a pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function The macro NULL expands to an implementation-defined

bcdiv using very small float with scientific notation cause “Division by zero” error

由 我是研究僧i 提交于 2019-12-06 04:09:55
Using bcdiv, i can't divide with small float using scientific notation : Working code : bcscale(30); $a = '1' ; $b = '0.00000001'; $result = bcdiv($a, $b); var_dump($result); Results in : string(20) "100000000.0000000000" Non-working code : bcscale(30); $a = '1' ; $b = '1e-8'; $result = bcdiv($a, $b); var_dump($result); Results in : Warning: bcdiv() [function.bcdiv]: Division by zero in C:\wamp\www\utilitaires\test_bcdiv.php on line XX NULL How can i do this division properly, with the less precision loss ? That is because, actually, bcmath doesn't support scientific notation. It isn't

Can an MD5-hash begin with a zero?

由 好久不见. 提交于 2019-12-05 18:11:56
问题 Can an MD5-hash begin with a zero? What about SHA-1? 回答1: Yes: $ echo -n "363" | md5sum 00411460f7c92d2124a67ea0f4cb5f85 - $ echo -n "351" | sha1sum 0026476a20bfbd08714155bb66f0b4feb2d25c1c Found by running the following in bash: for i in {1..1000} ; do echo $(echo -n $i | md5sum) $i ; done | sort | head 回答2: I found a MD5 hash that beginns with a zero byte! 2 character String Unicode #7358 #34823 $returnValue = md5('Ჾ蠇'); result: 00000000 5e0a51c8 313ffb43 8a3a2861 回答3: Of course. Or two
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