我真的不知道这方面的术语，我只是举个例子：
value_holder<float> floaty;
std::cout << floaty.is_integer << "\n";
这样当我做的时候
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<meta name="viewport" id="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no">
<title>Full Screen Slider - Jssor Slider</title>
<style>
html, body {
/*position: fixed;*/
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
</style>
</head>
<body style="font-family: Arial, Verdana, Sans-Serif;">
<script type="text/javascript" src="../js/jssor.slider-25.0.6.min.js"></script>
<script>
jssor_slider1_init = function () {
var options = {
$AutoPlay: 0, //[Optional] Auto play or not, to enable slideshow, this option must be set to greater than 0. Default value is 0. 0: no auto play, 1: continuously, 2: stop at last slide, 4: stop on click, 8: stop on user navigation (by arrow/bullet/thumbnail/drag/arrow key navigation)
$Idle: 1500, //[Optional] Interval (in milliseconds) to go for next slide since the previous stopped if the slider is auto playing, default value is 3000
$PauseOnHover: 1, //[Optional] Whether to pause when mouse over if a slider is auto playing, 0 no pause, 1 pause for desktop, 2 pause for touch device, 3 pause for desktop and touch device, 4 freeze for desktop, 8 freeze for touch device, 12 freeze for desktop and touch device, default value is 1
$DragOrientation: 1, //[Optional] Orientation to drag slide, 0 no drag, 1 horizental, 2 vertical, 3 either, default value is 1 (Note that the $DragOrientation should be the same as $PlayOrientation when $Cols is greater than 1, or parking position is not 0)
$ArrowKeyNavigation: 1, //[Optional] Steps to go for each navigation request by pressing arrow key, default value is 1.
$SlideDuration: 800, //Specifies default duration (swipe) for slide in milliseconds
$ArrowNavigatorOptions: { //[Optional] Options to specify and enable arrow navigator or not
$Class: $JssorArrowNavigator$, //[Requried] Class to create arrow navigator instance
$ChanceToShow: 2 //[Required] 0 Never, 1 Mouse Over, 2 Always
}
};
var jssor_slider1 = new $JssorSlider$('slider1_container', options);
//responsive code begin
//you can remove responsive code if you don't want the slider scales while window resizing
function ScaleSlider() {
var parentNode = jssor_slider1.$Elmt.parentNode;
var parentWidth = parentNode.clientWidth;
if (parentWidth) {
var parentHeight = parentNode.clientHeight;
jssor_slider1.$ScaleSize(parentWidth, parentHeight);
}
else {
$Jssor$.$Delay(ScaleSlider, 30);
}
}
ScaleSlider();
$Jssor$.$AddEvent(window, "load", ScaleSlider);
$Jssor$.$AddEvent(window, "resize", ScaleSlider);
$Jssor$.$AddEvent(window, "orientationchange", ScaleSlider);
//responsive code end
};
</script>
<!-- Jssor Slider Begin -->
<div style="position:relative;top:0;left:0;width:100%;height:100%;overflow:hidden;">
<div id="slider1_container" style="margin: 0 auto; position: relative; top: 0px; left: 0px; width: 800px;
height: 356px; background: #191919; overflow: hidden;">
<!-- Loading Screen -->
<div data-u="loading" style="position:absolute;top:0px;left:0px;background:url('../img/loading.gif') no-repeat 50% 50%; background-color: rgba(0, 0, 0, .7);"></div>
<!-- Slides Container -->
<div data-u="slides" style="position: absolute; left: 0px; top: 0px; width: 800px; height: 356px; overflow: hidden;">
<div>
<img u="image" src="../img/alila/01.jpg" />
</div>
<div>
<img u="image" src="../img/alila/02.jpg" />
</div>
<div>
<img u="image" src="../img/alila/03.jpg" />
</div>
<div>
<img u="image" src="../img/alila/04.jpg" />
</div>
<div>
<img u="image" src="../img/alila/05.jpg" />
</div>
<div>
<img u="image" src="../img/alila/06.jpg" />
</div>
<div>
<img u="image" src="../img/alila/07.jpg" />
</div>
<div>
<img u="image" src="../img/alila/08.jpg" />
</div>
<div>
<img u="image" src="../img/alila/09.jpg" />
</div>
<div>
<img u="image" src="../img/alila/10.jpg" />
</div>
<div>
<img u="image" src="../img/alila/11.jpg" />
</div>
<div>
<img u="image" src="../img/alila/12.jpg" />
</div>
</div>
<!--#region Arrow Navigator Skin Begin -->
<style>
/* jssor slider arrow navigator skin 05 css */
/*
.jssora05l (normal)
.jssora05r (normal)
.jssora05l:hover (normal mouseover)
.jssora05r:hover (normal mouseover)
.jssora05l.jssora05ldn (mousedown)
.jssora05r.jssora05rdn (mousedown)
.jssora05l.jssora05lds (disabled)
.jssora05r.jssora05rds (disabled)
*/
.jssora05l, .jssora05r {
display: block;
position: absolute;
/* size of arrow element */
width: 40px;
height: 40px;
cursor: pointer;
background: url(../img/a17.png) no-repeat;
overflow: hidden;
}
.jssora05l { background-position: -10px -40px; }
.jssora05r { background-position: -70px -40px; }
.jssora05l:hover { background-position: -130px -40px; }
.jssora05r:hover { background-position: -190px -40px; }
.jssora05l.jssora05ldn { background-position: -250px -40px; }
.jssora05r.jssora05rdn { background-position: -310px -40px; }
.jssora05l.jssora05lds { background-position: -10px -40px; opacity: .3; pointer-events: none; }
.jssora05r.jssora05rds { background-position: -70px -40px; opacity: .3; pointer-events: none; }
</style>
<!-- Arrow Left -->
<span u="arrowleft" class="jssora05l" style="top: 158px; left: 8px;">
</span>
<!-- Arrow Right -->
<span u="arrowright" class="jssora05r" style="top: 158px; right: 8px">
</span>
<!--#endregion Arrow Navigator Skin End -->
<!-- Trigger -->
<script>
jssor_slider1_init();
</script>
</div>
</div>
<!-- Jssor Slider End -->
<!-- remove the following if no need-->
<p>other content</p>
</body>
</html>
它会打印0
我如何定义成员is_integer以便这样做？
答案 0 :(得分：2)
您可以使用std::is_same来做到这一点
它遵循一个最小的工作示例：
#include<type_traits>
template <typename T>
struct value_holder {
T value;
static const bool is_integer = std::is_same<int, T>::value or std::is_same<long, T>::value;
};
int main() {
static_assert(value_holder<int>::is_integer, "!");
static_assert(not value_holder<char>::is_integer, "!");
}
另一种可能的方法是基于模板专业化。这种方式应该有效：
template <typename T>
struct value_holder {
T value;
static const bool is_integer = false;
};
template <>
struct value_holder<int> {
int value;
static const bool is_integer = true;
};
template <>
struct value_holder<long> {
long value;
static const bool is_integer = true;
};
无论如何，从我的观点来看，它有点冗长，如果你的班级包含多个数据成员，可能会很烦人。
答案 1 :(得分：2)
正如昆汀的回答所说，你使用了一种类型特征。 std::is_integral在您的示例中有意义：
template <typename T>
struct value_holder {
T value;
static constexpr bool is_integer = std::is_integral<T>::value;
};
但这并不完全符合您的评论。如果您确实希望is_integer仅对int或long成为真，那么您可以定义自定义类型特征：
template <typename T>
struct is_int_or_long : std::false_type {};
template <>
struct is_int_or_long<int> : std::true_type {};
template <>
struct is_int_or_long<long> : std::true_type {};
template <typename T>
struct value_holder {
T value;
static constexpr bool is_integer = is_int_or_long<T>::value;
};
当然，使用std::is_same特征可以缩短这一点：
template <typename T>
struct value_holder {
T value;
static constexpr bool is_integer = std::is_same<T, int>::value || std::is_same<T, long>::value;
};
答案 2 :(得分：0)
您正在寻找类型特征。您可能会对std::is_integral感兴趣。