auto

Hibernate配置文件的hbm2ddl.auto属性

由 泄露秘密 提交于 2019-12-19 05:22:39
今天遇到一个有意思的问题，我目前做的一个网站采用Spring MVC + Spring + Hibernate的架构，我通过页面插入了一些数据到数据库，可是每次重启tomcat之后，数据都莫名其妙地丢失了，但是我确定数据库中原本是有数据的，数据一定是在应用服务器重启之后被清除的，百思不得其解，忽然想到有可能是昨天修改了Hibernate配置文件导致的。 我的Hibernate配置文件： <hibernate-configuration> <session-factory> <property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property> <property name="hibernate.show_sql">true</property> <property name="hbm2ddl.auto">create</property> </session-factory> </hibernate-configuration> 问题就出在我把hbm2ddl.auto的值设为create了，根据Hibernate的文档，hbm2ddl.auto有四个可选值： 值 定义 update 最常用的值，第一次加载hibernate时根据model类会自动建立起表的结构（前提是先建立好数据库）

overflow --百度百科

由 扶醉桌前 提交于 2019-12-18 20:19:38
【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> overflow CSS属性 overflow 为CSS中设置当对象的内容超过其指定高度及宽度时如何管理内容的属性。 基本特性 初始值： visible 适用于： block-level and replaced elements 继承性： 无 百分比： N/A 媒体： visual 版本： CSS2 兼容性： IE4+ NS6+ 基本语法 overflow-x overflow-y overflow : visible | auto | hidden | scroll 语法取值 visible : 默认值。不剪切内容也不添加滚动条。假如显式声明此默认值， 对象将以包含对象的 window 或 frame 的尺寸裁切。并且 clip 属性设置将失效 auto : 在必需时对象内容才会被裁切或显示滚动条 hidden : 不显示超过对象尺寸的内容 scroll : 总是显示滚动条 清除浮动 设置overflow的一个更流行的用处是，清除浮动。设置overflow并不会在该元素上 清除浮动，它将清除自己(self-clear)。意思就是，应用了overflow(auto或hidden)的元素，将会扩展到它需要的大小以包围它 里面的浮动的子元素(而不是叠了起来(collapsing))，假设未定义高度。就像这样：

vector<bool>::operator[] misbehavior? [duplicate]

由 一曲冷凌霜 提交于 2019-12-18 16:11:14
问题 This question already has answers here : Closed 6 years ago . Possible Duplicate: Why vector<bool>::reference doesn’t return reference to bool? I used to think that with std::vector::operator[] we get deep copies of the accessed item, but it seems that it is not always true. At least, with vector<bool> the following test code gives a different result: #include <iostream> #include <vector> using namespace std; template <typename T> void Test(const T& oldValue, const T& newValue, const char*

Variable template in template class - unexpected error (possible bug?)

由 与世无争的帅哥 提交于 2019-12-18 14:12:56
问题 Having: struct Value { template<class T> static constexpr T value{0}; }; (0) ideone template<typename TValue> struct Something { void x() { static_assert(TValue::template value<int> == 0, ""); } }; int main() { Something<Value>{}.x(); return 0; } Does not compile with clang++ 3.6. error: cannot refer to variable template 'value' without a template argument list Does not compile with g++ 5.2. error: ‘template constexpr const T Value::value’ is not a function template (1) ideone Compiles with

Erasing item in a for(-each) auto loop

由 怎甘沉沦 提交于 2019-12-18 04:18:12
问题 Is there a way to erase specific elements when using a auto variable in a for loop like this? for(auto a: m_Connections) { if(something) { //Erase this element } } I know I can either do say for(auto it=m_map.begin() ... or for(map<int,int>::iterator it=m_map.begin() ... and manually increment the iterator (and erase) but if I could do it with less lines of code I'd be happier. Thanks! 回答1: No, there isn't. Range based for loop is used to access each element of a container once. Every time an

auto with string literals

由 老子叫甜甜 提交于 2019-12-18 03:04:48
问题 #include <iostream> #include <typeinfo> int main() { const char a[] = "hello world"; const char * p = "hello world"; auto x = "hello world"; if (typeid(x) == typeid(a)) std::cout << "It's an array!\n"; else if (typeid(x) == typeid(p)) std::cout << "It's a pointer!\n"; // this is printed else std::cout << "It's Superman!\n"; } Why is x deduced to be a pointer when string literals are actually arrays? A narrow string literal has type "array of n const char " [2.14.5 String Literals [lex.string]

How to use lambda auto parameters in C++11

由 做~自己de王妃 提交于 2019-12-17 23:24:49
问题 I have a code in C++14. However, when I used it in C++11, it has an error at const auto . How to use it in C++11? vector<vector <int> > P; std::vector<double> f; vector< pair<double, vector<int> > > X; for (int i=0;i<N;i++) X.push_back(make_pair(f[i],P[i])); ////Sorting fitness descending order stable_sort(X.rbegin(), X.rend()); std::stable_sort(X.rbegin(), X.rend(), [](const auto&lhs, const auto& rhs) { return lhs.first < rhs.first; }); 回答1: C++11 doesn't support generic lambdas . That's

The relationship between auto and decltype

由 此生再无相见时 提交于 2019-12-17 22:05:51
问题 Is auto x = initializer; equivalent to decltype(initializer) x = initializer; or decltype((initializer)) x = initializer; or neither? 回答1: decltype also considers whether the expression is rvalue or lvalue . Wikipedia says, The type denoted by decltype can be different from the type deduced by auto. #include <vector> int main() { const std::vector<int> v(1); auto a = v[0]; // a has type int decltype(v[0]) b = 1; // b has type const int&, the return type of // std::vector<int>::operator[](size

undefined behaviour somewhere in boost::spirit::qi::phrase_parse

由 大憨熊 提交于 2019-12-17 06:56:23
问题 I am learning to use boost::spirit library. I took this example http://www.boost.org/doc/libs/1_56_0/libs/spirit/example/qi/num_list1.cpp and compiled it on my computer - it works fine. However if I modify it a little - if I initialize the parser itself auto parser = qi::double_ >> *(',' >> qi::double_); somewhere as global variable and pass it to phrase_parse, everything goes crazy. Here is the complete modified code (only 1 line is modified and 1 added) - http://pastebin.com/5rWS3pMt If I

Advantages of auto in template parameters in C++17

由 若如初见. 提交于 2019-12-17 03:04:34
问题 What are the advantages of auto in template parameters that will (possibly) be introduced with C++17? Is it just a natural extension of auto when I want to instantiate template code? auto v1 = constant<5>; // v1 == 5, decltype(v1) is int auto v2 = constant<true>; // v2 == true, decltype(v2) is bool auto v3 = constant<'a'>; // v3 == 'a', decltype(v3) is char What else do I gain from this language feature? 回答1: The template <auto> feature (P0127R1) was accepted into C++ in the ISO C++ 2016
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