map

Why does setting an element of a map to its size increments the size *before* assigning it?

由 送分小仙女□ 提交于 2020-05-11 04:52:41
问题 This is a common pattern I use to index tokens as they come in: check if the token is in a map, and if not, add it to the map, assigning the map's size. When doing this in C++, it unexpectedly increments the map's size before the assignment is made: #include <cstdio> #include <map> using namespace std; int main() { map<char, int> m; printf("Size before adding: %d\n", m.size()); m['A'] = m.size(); printf("Size after adding: %d\n", m.size()); printf("What was added: %d\n", m['A']); return 0; }

Why does setting an element of a map to its size increments the size *before* assigning it?

由 霸气de小男生 提交于 2020-05-11 04:52:24
问题 This is a common pattern I use to index tokens as they come in: check if the token is in a map, and if not, add it to the map, assigning the map's size. When doing this in C++, it unexpectedly increments the map's size before the assignment is made: #include <cstdio> #include <map> using namespace std; int main() { map<char, int> m; printf("Size before adding: %d\n", m.size()); m['A'] = m.size(); printf("Size after adding: %d\n", m.size()); printf("What was added: %d\n", m['A']); return 0; }

Why does setting an element of a map to its size increments the size *before* assigning it?

由 落爺英雄遲暮 提交于 2020-05-11 04:51:59
问题 This is a common pattern I use to index tokens as they come in: check if the token is in a map, and if not, add it to the map, assigning the map's size. When doing this in C++, it unexpectedly increments the map's size before the assignment is made: #include <cstdio> #include <map> using namespace std; int main() { map<char, int> m; printf("Size before adding: %d\n", m.size()); m['A'] = m.size(); printf("Size after adding: %d\n", m.size()); printf("What was added: %d\n", m['A']); return 0; }

在谷歌地图上显示地名等信息，类似infowindow

由 纵饮孤独 提交于 2020-04-21 06:47:33
function Tooltip(options) { this.marker_ = options.marker; this.content_ = options.content; this.map_ = options.marker.get('map'); this.cssClass_ = options.cssClass || null; this.is_hidden = options.is_hidden === undefined ? !0 : options.is_hidden; this.div_ = null; this.setMap(this.map_); var me = this; if(this.is_hidden){ google.maps.event.addDomListener(me.marker_, 'mouseover', function(){ me.show(); }); google.maps.event.addDomListener(me.marker_, 'mouseout', function(){ me.hide(); }); } } Tooltip.prototype = new google.maps.OverlayView(); Tooltip.prototype.onAdd = function() { var div =

EXC_BAD_ACCESS(code=1, address=0x0) occurs when passing a std::map as parameter to a virtual function call

由 风格不统一 提交于 2020-04-18 07:34:12
问题 I have a class that has the following virtual function namespace Book { class Secure { virtual Result setPassword(const std::map<std::string, std::vector<std::string> >& params)=0; } } I have another test class in which a method gets the password and user name from the excel and sets it to the map secureParams and sets the password for the current file. bool initialize(std::string bookPath, std::string loginPath, std::string userName, std::string password) { Book::SharedPtr<Book::Secure>

State Plane Coordinate to Latitude Longitude

由 眉间皱痕 提交于 2020-04-18 06:47:45
问题 I search for a C++/C# library or tool they can convert State Plane Coordinate to latitude/longitude. Thanks 回答1: You want PROJ, the Cartographic Projections Library: https://proj.org/index.html This used to be referred to as "PROJ4" but is now "PROJ". 来源： https://stackoverflow.com/questions/15237804/state-plane-coordinate-to-latitude-longitude

python内置函数map/reduce/filter

由 本秂侑毒 提交于 2020-04-07 11:35:23
python有几个内置的函数很有意 思：map/filter/reduce，都是对一个集合进行处理，filter很容易理解用于过滤，map用于映射，reduce用于归并。 是python列表方法的三架马车。 filter() 函数: filter 函数的功能相当于过滤器。调用一个布尔函数bool_func来迭代遍历每个seq中的元素；返回一个使bool_seq返回值为true的元素的序列。 >>>a=[1,2,3,4,5,6,7] >>>b=filter(lambda x:x>5, a) >>>print b >>>[6,7] 如果filter参数值为None，就使用identity（）函数，list参数中所有为假的元 素都将被删除。如下所示： >>>a=[0,1,2,3,4,5,6,7] >>>b=filter(None, a) >>>print b >>>[1,2,3,4,5,6,7] map() 函数： map函数func作用于给定序列的每个元素，并用一个列表来提供返回值。 >>>map(lambda x:x+3, a) #这里的a同上 >>>[3,4,5,6,7,8,9,10] #另一个例子 >>>a=[1,2,3] >>>b=[4,5,6] >>>map(lambda x,y:x+y, a,b) >>>[5,7,9] reduce() 函数： reduce函数

集合类操作优化经验总结(三)

由 瘦欲@ 提交于 2020-03-24 16:36:01
3 月，跳不动了？>>> 集合类实践 ArrayList、Vector、LinkedList 均来自 AbstractList 的实现，而 AbstractList 直接实现了 List 接口，并扩展自 AbstarctCollection。ArrayList 和 Vector 使用了数组实现，ArrayList 没有对任何一个方法提供线程同步，因此不是线程安全的，Vector 中绝大部分方法都做了线程同步，是一种线程安全的实现。LinkedList 使用了循环双向链表数据结构，由一系列表项连接而成，一个表项总是包含 3 个部分，元素内容、前驱表项和后驱表项。 当 ArrayList 对容量的需求超过当前数组的大小时，需要进行扩容。扩容过程中，会进行大量的数组复制操作，而数组复制时，最终将调用 System.arraycopy() 方法。LinkedList 由于使用了链表的结构，因此不需要维护容量的大小，然而每次的元素增加都需要新建一个 Entry 对象，并进行更多的赋值操作，在频繁的系统调用下，对性能会产生一定的影响，在不间断地生成新的对象还是占用了一定的资源。而因为数组的连续性，因此总是 在尾端增加元素时，只有在空间不足时才产生数组扩容和数组复制。 ArrayList 是基于数组实现的，而数组是一块连续的内存空间，如果在数组的任意位置插入元素

GUAVA常用方法总结整理（list map string concurrent file）

由 无人久伴 提交于 2020-03-19 14:59:33
3 月，跳不动了？>>> 1.对字符串的操作： package com.wenniuwuren.guava; import java.io.UnsupportedEncodingException; import java.util.Date; import java.util.HashMap; import com.google.common.base.CharMatcher; import com.google.common.base.Charsets; import com.google.common.base.Objects; import com.google.common.base.Strings; import com.google.common.collect.ComparisonChain; import sun.org.mozilla.javascript.internal.ast.TryStatement; /** * * @ClassName: WorkingWithStrings * @Description: 对字符串的操作 * @author wenniuwuren * @date 2015-5-20 上午11:33:59 * */ public class WorkingWithStrings { public static void main

GUAVA常用方法总结整理（list map string concurrent file）

由 纵饮孤独 提交于 2020-03-19 14:30:17
3 月，跳不动了？>>> 1.对字符串的操作： package com.wenniuwuren.guava; import java.io.UnsupportedEncodingException; import java.util.Date; import java.util.HashMap; import com.google.common.base.CharMatcher; import com.google.common.base.Charsets; import com.google.common.base.Objects; import com.google.common.base.Strings; import com.google.common.collect.ComparisonChain; import sun.org.mozilla.javascript.internal.ast.TryStatement; /** * * @ClassName: WorkingWithStrings * @Description: 对字符串的操作 * @author wenniuwuren * @date 2015-5-20 上午11:33:59 * */ public class WorkingWithStrings { public static void main
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