我们假设我使用参数包重新创建printf：
void printf(const char* string)
{
std::cout << string;
}
template <typename T, typename... Params>
void printf(const char* string, T first, Params... p)
{
while (*string != '\0')
{
if (*string == '%' && *(string + 1) != '%')
{
std::cout << first;
string += 2;
printf(string, p...);
return;
}
std::cout << *string++;
}
}
我使用以下参数调用该函数：
printf("%d is the answer to life, the universe, and everything. Pi = %f", 42, 3.14);
编译器是否会创建具有不同签名的2个不同函数？
printf(const char*, int, Params...);
和printf(const char*, double, Params...);
如果是这样，带有10个参数的函数调用将导致创建10个不同的函数。编译器是否对此进行了优化？
答案 0 :(得分：4)
我希望通过此调用得到以下两个模板实例：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Markup;
namespace Infinity.Shell.Controls.Docking
{
/// <summary>
/// Follow steps 1a or 1b and then 2 to use this custom control in a XAML file.
///
/// Step 1a) Using this custom control in a XAML file that exists in the current project.
/// Add this XmlNamespace attribute to the root element of the markup file where it is
/// to be used:
///
/// xmlns:MyNamespace="clr-namespace:Infinity.Shell.Controls.Docking"
///
///
/// Step 1b) Using this custom control in a XAML file that exists in a different project.
/// Add this XmlNamespace attribute to the root element of the markup file where it is
/// to be used:
///
/// xmlns:MyNamespace="clr-namespace:Infinity.Shell.Controls.Docking;assembly=Infinity.Shell.Controls.Docking"
///
/// You will also need to add a project reference from the project where the XAML file lives
/// to this project and Rebuild to avoid compilation errors:
///
/// Right click on the target project in the Solution Explorer and
/// "Add Reference"->"Projects"->[Browse to and select this project]
///
///
/// Step 2)
/// Go ahead and use your control in the XAML file.
///
/// <MyNamespace:SplitContainer/>
///
/// </summary>
public class SplitContainer : Control
{
public Orientation Orientation
{
get { return (Orientation)GetValue(OrientationProperty); }
set { SetValue(OrientationProperty, value); }
}
// Using a DependencyProperty as the backing store for MyProperty. This enables animation, styling, binding, etc...
public static readonly DependencyProperty OrientationProperty =
DependencyProperty.Register("Orientation", typeof(Orientation), typeof(SplitContainer), new PropertyMetadata(Orientation.Horizontal));
public UIElement FirstChild
{
get { return (UIElement)GetValue(FirstChildProperty); }
set { SetValue(FirstChildProperty, value); }
}
// Using a DependencyProperty as the backing store for MyProperty. This enables animation, styling, binding, etc...
public static readonly DependencyProperty FirstChildProperty =
DependencyProperty.Register("FirstChild", typeof(UIElement), typeof(SplitContainer), new PropertyMetadata(null));
public UIElement SecondChild
{
get { return (UIElement)GetValue(SecondChildProperty); }
set { SetValue(SecondChildProperty, value); }
}
// Using a DependencyProperty as the backing store for MyProperty. This enables animation, styling, binding, etc...
public static readonly DependencyProperty SecondChildProperty =
DependencyProperty.Register("SecondChild", typeof(UIElement), typeof(SplitContainer), new PropertyMetadata(null));
static SplitContainer()
{
DefaultStyleKeyProperty.OverrideMetadata(typeof(SplitContainer), new FrameworkPropertyMetadata(typeof(SplitContainer)));
}
public override void OnApplyTemplate()
{
base.OnApplyTemplate();
}
}
}
<Style TargetType="{x:Type dock:SplitContainer}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type dock:SplitContainer}">
<Border Background="{TemplateBinding Background}"
BorderBrush="{TemplateBinding BorderBrush}"
BorderThickness="{TemplateBinding BorderThickness}">
<Grid>
<Grid.RowDefinitions>
<RowDefinition/>
<RowDefinition Height="Auto"/>
<RowDefinition/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions> <!--Horizontal -->
<ColumnDefinition/>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<Grid x:Name="PART_FirstChildGrid"
Grid.Column="0"
Grid.Row="0"
Grid.RowSpan="3">
<ContentPresenter Content="{TemplateBinding FirstChild}"/>
</Grid>
<GridSplitter x:Name="PART_Splitter"
Grid.Column="1"
Grid.Row="0"
Grid.RowSpan="3"
Grid.ColumnSpan="1"
Width="5"
VerticalAlignment="Stretch"
HorizontalAlignment="Center"
ShowsPreview="True"/>
<Grid x:Name="PART_SecondChildGrid"
Grid.Column="2"
Grid.Row="0"
Grid.RowSpan="3">
<ContentPresenter Content="{TemplateBinding SecondChild}"/>
</Grid>
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="Orientation" Value="Vertical">
<Setter TargetName="PART_FirstChildGrid" Property="Grid.Column" Value="0"/>
<Setter TargetName="PART_FirstChildGrid" Property="Grid.Row" Value="0"/>
<Setter TargetName="PART_FirstChildGrid" Property="Grid.ColumnSpan" Value="3"/>
<Setter TargetName="PART_FirstChildGrid" Property="Grid.RowSpan" Value="1"/>
<Setter TargetName="PART_Splitter" Property="Grid.Column" Value="0"/>
<Setter TargetName="PART_Splitter" Property="Grid.Row" Value="1"/>
<Setter TargetName="PART_Splitter" Property="Grid.ColumnSpan" Value="3"/>
<Setter TargetName="PART_Splitter" Property="Grid.RowSpan" Value="1"/>
<Setter TargetName="PART_Splitter" Property="VerticalAlignment" Value="Center"/>
<Setter TargetName="PART_Splitter" Property="HorizontalAlignment" Value="Stretch"/>
<Setter TargetName="PART_Splitter" Property="Width" Value="Auto"/>
<Setter TargetName="PART_Splitter" Property="Height" Value="5"/>
<Setter TargetName="PART_SecondChildGrid" Property="Grid.Column" Value="0"/>
<Setter TargetName="PART_SecondChildGrid" Property="Grid.Row" Value="2"/>
<Setter TargetName="PART_SecondChildGrid" Property="Grid.ColumnSpan" Value="3"/>
<Setter TargetName="PART_SecondChildGrid" Property="Grid.RowSpan" Value="1"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:Infinity.Shell.Controls.Text;assembly=Infinity.Shell"
xmlns:dock="clr-namespace:Infinity.Shell.Controls.Docking;assembly=Infinity.Shell"
x:Class="Infinity.MainWindow"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="499.573" Background="#FF1E1E1E">
<Grid>
<dock:SplitContainer Orientation="Vertical">
<dock:SplitContainer.FirstChild>
<dock:SplitContainer>
<dock:SplitContainer.FirstChild>
<Button Content="First Child Button"/>
</dock:SplitContainer.FirstChild>
<dock:SplitContainer.SecondChild>
<Button Content="Second Child Button"/>
</dock:SplitContainer.SecondChild>
</dock:SplitContainer>
</dock:SplitContainer.FirstChild>
<dock:SplitContainer.SecondChild>
<Button Content="First Splitter Second Child"/>
</dock:SplitContainer.SecondChild>
</dock:SplitContainer>
</Grid>
</Window>
和
printf(const char*, int, double);
而且，是的，如果将11个参数传递给此printf(const char*, double);
，编译器将生成10个模板函数实例。这就是为什么模板因创建代码膨胀而享有声誉的原因。
如果有，请说
printf()我希望两个模板实例都是相同的，并在链接时合并在一起。但这是一个小小的安慰。