size | 易学教程

mongodb进阶一之高级查询

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这篇我们来说说mongodb的进阶--------------高级查询一：各种查询 1：条件操作符 <, <=, >, >= 这个操作符就不用多解释了，最常用也是最简单的。 db.collection.find({ “field” : { $gt: value } } ); // 大于: field > value db.collection.find({ “field” : { $lt: value } } ); // 小于: field < value db.collection.find({ “field” : { $gte: value } } ); // 大于等于: field >= value db.collection.find({ “field” : { $lte: value } } ); // 小于等于: field <= value 如果要同时满足多个条件，可以这样做 db.collection.find({ “field” : { $gt: value1, $lt: value2 } } ); // value1 < field < value2 为了练习，我们先插几条数据 db.users.insert([{name:“Tom”,age:20,sex:“m”},{name:“Lily”,age:40,sex:“f”},{name:“Suby”,age

RSA encryption using public key. Data size based on key

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问题 I'm using the OpenSSL RSA API to encrypt data with a server's public key. uint32_t rsasize = RSA_size(keypair); // -- RSA key size == 256 uint32_t dl = 255 uint8_t *d; // points to 255 bytes of data unsigned char *encrypt = (unsigned char*)malloc(rsasize); auto num = RSA_public_encrypt(dl, d, encrypt, keypair, RSA_NO_PADDING); if ( num == -1 ) { auto err = malloc(130); ERR_load_crypto_strings(); ERR_error_string(ERR_get_error(), (char*)err); printf("Error encrypting message: %s\n", err);

Android custom dialog linearlayout size same as dialogs bg image

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问题 I am creating a custom dialog as: Dialog myDialog = new Dialog(context, R.style.Theme_Levels); myDialog.setContentView(R.layout.levelselector); myDialog.show(); Style used: <style name="Theme.Levels" parent="@android:style/Theme.Dialog"> <item name="android:windowFrame">@null</item> <item name="android:windowIsFloating">true</item> <item name="android:windowBackground">@drawable/dlgbg</item> <item name="android:windowContentOverlay">@null</item> <item name="android:windowSoftInputMode"

Freeze in C++ program using huge vector

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问题 I have an issue with a C++ program. I think it's a problem of memory. In my program i'm used to create some enormous std::vector (i use reserve to allocate some memory). With vector size of 1 000 000, it's ok but if i increase this number (about ten millions), my program will freeze my PC and i can do nothing except waiting for a crash (or end of the program if i'm lucky). My vector contains a structure called Point which contain a vector of double. I used valgrind to check if there is a

Fread number of bytes limit

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问题 Does fread have a limit for the number of bytes it can read at once? Or I can read any size I would like to charge in to my pointer? For example, Can I read file of 50MB once using fread to charge it into char pointer? 回答1: Theoretically, yes, it can read any number of bytes up to the maximum of size_t (which is an unsigned int (roughly 4GB on a 32-bit system). However, since your buffer will have to be allocated in a contiguous block, it is not likely to be feasible, nor advisable, to read

Size limit of my ios app particularly Core Data

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问题 I have developed an app. It is an in-house app. I want to know if there is any limit on the size my app can take up on the iOS device. My app connects to a web-service and downloads data from SQL server. Maybe 1000s of rows. How much data can my app store on the iOS device? Can someone explain it in simple terms. I read its 2GB. But i think that is the size of the app when you install it.Correct? In archives section of organizer my app now says 1MB. So that 2gb, is the limit there correct?50

Different lucene search results using different search space size

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问题 I have an application that uses lucene for searching. The search space are in the thousands. Searching against these thousands, I get only a few results, around 20 (which is ok and expected). However, when I reduce my search space to just those 20 entries (i.e. I indexed only those 20 entries and disregard everything else...so that development would be easier), I get the same 20 results but in different order (and scoring). I tried disabling the norm factors via Field#setOmitNorms(true), but

iOS自定义弹出视图

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/*--> */ /*--> */ 里面的坐标可能有问题可以自己修改 #define kSelfBackgroundColor [UIColor colorWithRed: 0 green: 0 blue: 0 alpha: 0.5f ]; #import "HBActionSheet.h" @interface HBActionSheet () @property ( nonatomic , strong ) UIView *btnBgView; @property ( nonatomic , strong ) UIButton *selectedBtn; @end @implementation HBActionSheet - ( instancetype )initWithFrame:( CGRect )frame { self = [ super initWithFrame :frame]; if ( self ) { self . frame = [ UIScreen mainScreen ]. bounds ; UIView *view = [[ UIView alloc ] initWithFrame : CGRectMake ( 0 , 0 , [ UIScreen mainScreen ]. bounds . size . width , 368 - 64 )]

Android Apps design resolution

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问题 I'm required to design an apps for android. And after some reading, I find out android device are divided into few categories in term of resolution, like small screen normal screen large screen extra large screen but in different density. So lets say, now I need to come out a design for normal screen, what resolution that I should use for the "look & feel" of the apps UI. From the reading, I know android apps are use dp instead of px. So, is it means I have to convert few specific screen size

How do I set minimum allowable width/height for widget/layout in Kivy?

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问题 I have BoxLayout with 3 elements, I need that first and last elements to occupy minimum available space. Middle element has fixed proportion (1:1), so when I resize the window, side elements become too small and content go out of it. I need e.g. label's (or button's, or even set's of different elements) text to be always inside the label. This size shouldn't be more, so I can say it should be fixed size depending on its content. UPDATE : I've made a mistake, size can be more , but not less.