auto

Return type deduction for in-class friend functions

大城市里の小女人 提交于 2020-01-21 02:36:10
问题 Here is a little experiment with return type deduction for in-class friend functions (using Clang 3.4 SVN and g++ 4.8.1 with std=c++1y in both cases) that is not documented in the linked working paper #include <iostream> struct A { int a_; friend auto operator==(A const& L, A const& R) { return L.a_ == R.a_; // a_ is of type int, so should return bool } }; template<class T> struct B { int b_; friend auto operator==(B const& L, B const& R) { return L.b_ == R.b_; // b_ is of type int, so should

Keras_callback

与世无争的帅哥 提交于 2020-01-19 04:00:36
1.ReduceLROnPlateau keras.callbacks.ReduceLROnPlateau(monitor='val_loss', factor=0.1, patience=10, verbose=0, mode='auto', epsilon=0.0001, cooldown=0, min_lr=0) 当评价指标不在提升时,减少学习率 当学习停滞时,减少2倍或10倍的学习率常常能获得较好的效果。该回调函数检测指标的情况,如果在patience个epoch中看不到模型性能提升,则减少学习率 2.ModelCheckpoint keras.callbacks.ModelCheckpoint(filepath,monitor='val_loss',verbose=0,save_best_only=False, save_weights_only=False, mode='auto', period=1) filepath:字符串,保存模型的路径(可以将模型的准确率和损失等写到路径中,格式如下:) ModelCheckpoint('model_check/'+'ep{epoch:d}-acc{acc:.3f}- val_acc{val_acc:.3f}.h5',monitor='val_loss') 还可以添加损失值等如 ‘loss{loss:.3f}-val_loss

CSS进阶

天涯浪子 提交于 2020-01-19 03:39:18
css选择器二 4、id选择器 通过id名来选择元素,元素的id名称不能重复,所以一个样式设置项只能对应于页面上一个元素,不能复用,id名一般给程序使用,所以不推荐使用id作为选择器。 举例: #box{color:red} ...... <p id="box">这是一个段落标签</p> <!-- 对应以上一条样式,其它元素不允许应用此样式 --> <p>这是第二个段落标签</p> <!-- 无法应用以上样式,每个标签只能有唯一的id名 --> <p>这是第三个段落标签</p> <!-- 无法应用以上样式,每个标签只能有唯一的id名 --> 5、组选择器 多个选择器,如果有同样的样式设置,可以使用组选择器。 举例: .box1,.box2,.box3{width:100px;height:100px} .box1{background:red} .box2{background:pink} .box2{background:gold} <div class="box1">....</div> <div class="box2">....</div> <div class="box3">....</div> 6、伪类选择器 常用的伪类选择器有hover,表示鼠标悬浮在元素上时的状态。 .box1:{width:100px;height:100px;background:gold;}

c++ auto关键字

痞子三分冷 提交于 2020-01-13 16:56:32
一些关于C++的出版物写到:我们经常会用到一些赋值操作,例如int a=6,前提是我们知道变量的类型。-----但我们经常不知道变量的类型,因此就要允许c++编译器帮我们判断变量类型,由此auto变量应孕而生 一般用法 #include<iostream> using namespace std; int main() { auto i = 888; auto coachname = "陈培昌"; int myarray[5] = {7,8,5,48,32}; cout << i<<endl; cout << coachname << endl; } 输出结果: 一些应用场景:循环打印数组元素 #include<iostream> using namespace std; int main() { int myarray[5] = {7,8,5,48,32}; for (auto wenwa : myarray) { cout << wenwa << endl; } return 0; } 输出结果: 一些使用问题----批量赋值的时候,尽量保持变量类型一致,否则报错 #include<iostream> using namespace std; int main() { auto name = "付高峰", i = 666; return 0; } 输出结果: 更改

Why would they special-case certain initializer lists instead of treating them all the same?

倖福魔咒の 提交于 2020-01-13 14:12:10
问题 Say I have a variable auto x that I want to initialize to 7 using brace initialization, simple: auto x {7}; Except I learned that x is NOT an integer, but an initialization list itself. Why? Is there a specific reason why the committee would decide that auto should grab the initialization list in the case of a single auto value, or do they expect us to just realize these shouldn't be used together. I cant seem to think of a possible reason i would want an initializer list to be stored into

OSG QT :获取鼠标的world坐标

假装没事ソ 提交于 2020-01-13 00:28:15
网上的代码大部分是这样的: 1 auto matViewMatrix = camera->getViewMatrix(); 2 auto matProjectionMatrix = camera->getProjectionMatrix(); 3 auto wndMatrix = camera->getViewport()->computeWindowMatrix(); 4 osg::Matrix MVPW = matViewMatrix * matProjectionMatrix * wndMatrix; 5 osg::Matrix inverseMVPW = osg::Matrix::inverse(MVPW); 6 osg::Vec3 mouseWorld = osg::Vec3(x,y, 0) * inverseMVPW; 在和QT结合的开发的时候,发现这个位置是错误的,因为是鼠标获取的坐标的原点是左上角,而OSG的世界坐标系的原点是左下角,所以要把鼠标的Y值做转换。 像下面这样的: 1 void GraphicsWinQt::mouseMoveEvent( QMouseEvent *event ) 2 { 3 setKeyboardModifiers( event ); 4 this->getEventQueue()->mouseMotion(event->x(),

Compiler can't deduce the return type?

会有一股神秘感。 提交于 2020-01-11 00:57:50
问题 I am trying to use the decltype keyword on an auto function: struct Thing { static auto foo() { return 12; } using type_t = decltype(foo()); }; And I get the following error (gcc 7.4): <source>:6:25: error: use of 'static auto Thing::foo()' before deduction of 'auto' decltype(foo()); ^ <source>:6:25: error: use of 'static auto Thing::foo()' before deduction of 'auto' Why has the compiler not yet deduced the return type? 回答1: Because for class definition, compiler will first determine all

Why does a range-based for statement take the range by auto&&?

三世轮回 提交于 2020-01-10 17:48:40
问题 A range-based for statement is defined in §6.5.4 to be equivalent to: { auto && __range = range-init; for ( auto __begin = begin-expr, __end = end-expr; __begin != __end; ++__begin ) { for-range-declaration = *__begin; statement } } where range-init is defined for the two forms of range-based for as: for ( for-range-declaration : expression ) => ( expression ) for ( for-range-declaration : braced-init-list ) => braced-init-list (the clause further specifies the meaning of the other sub

z-index下的一些知识

会有一股神秘感。 提交于 2020-01-10 01:43:00
前几天工作的时候遇到一个问题,在IE6下select 这个控件似乎无法用z-index 属性隐藏,接下来就开始了寻找问题的解法,总结了一些z-index 的知识。 z-index 定义和用法 z-index 属性设置元素的堆叠顺序。拥有更高堆叠顺序的元素总是会处于堆叠顺序较低的元素的前面。该属性设置一个定位元素沿z 轴的位置,z 轴定义为垂直延伸到显示区的轴。如果为正数,则离用户更近,为负数则表示离用户更远。——W3shcool z-index:auto | number 默认值:auto 堆叠顺序与父元素相等 number:无单位的整数值,可为负数 JavaScript 语法: object.style.zIndex=”1″ 注意: z-index 属性适用于那些被定义了除position:static 外任意属性的元素中。即z-index 仅能在定位元素上奏效(position: absolute | relative | fix)。 stacking context & stack level & z-index 是什么 stacking context 堆叠上下文 每个定位元素都归属于一个stacking context(即堆叠上下文,以下统一用堆叠上下文),最初的堆叠上下文(即根部堆叠上下文)是由根元素产生(一般页面的根元素是body),而其他的堆叠上下文则由定位元素产生

Effective C++: auto类型推断.

霸气de小男生 提交于 2020-01-08 23:32:31
【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> 1,请牢牢记住一点auto的推断其实是跟template的推断基本一致也有稍微的不同体现在std::initializer_list: 2,不能推断出一个模板中的另一个模板的类型(template<template<typenaem T> class A>); 3, 当auto作为函数的参数类型或者返回类型的时候auto类型的推断规则无效!按照模板类型的推断规则来. case 1: auto #include <iostream> int main() { int x = 27; int& xx = x; const int cx = x; const int& rx = x; auto n_ = 10; //auto = int; auto x_ = x; //auto = int; auto xx_ = x;//auto = int; xx_ = 100; std::cout<<x<<std::endl; auto cx_ = cx; //auto = int; auto rx_ = rx; //auto = int; cx_ = 10; //ok, but x is also 27. rx_ = 100;//as same sa above. return 0; } case 2: auto&