Question

我正在尝试复制传递给复制构造函数的对象。我想访问传递给此函数的对象的成员变量的解引用值，但遇到错误“在'（'令牌int * c = new int（other。（* pa））之前出现预期的unqualified-id；

该类已定义：

class Foo {
Public:
   int *a, *b;
   Foo(const Foo &); //copy constructor
}

我的功能已定义：

Foo::Foo(const Foo& other) {
    int* c = new int(other.(*a));
    int* d = new int(other.(*b));
 }

主要定义：

Foo first(1,2);
Foo second(first);

Answer 1

复制构造函数看起来像

Foo::Foo(const Foo& other) : a( new int( *other.a ) ), b( new int( *other.b ) )
{
}

这是一个演示程序

#include <iostream>

class Foo {
public:
   int *a, *b;

   Foo( int x, int y ) : a( new int( x ) ), b( new int( y ) )
   {
   }

   Foo( const Foo &other  ) : a( new int( *other.a ) ), b( new int( *other.b ) )
   {
   }
};

int main() 
{
    Foo first(1,2);
    Foo second(first); 

    std::cout << *first.a << ", " << *first.b << '\n';
    std::cout << *second.a << ", " << *second.b << '\n';

    return 0;
}

其输出为

1, 2
1, 2

所有其他特殊成员函数，例如析构函数，我希望您可以定义自己。

Answer 2

将值分配给对象成员。

library(tidyverse)
library(ggplot2)
library(shiny)
library(leaflet)
library(leafpop)


id <- c(1,1,1,1,2,2,3,3,3,4)
lat <- c(49.823, 49.823, 49.823, 49.823, 58.478, 58.478, 57.478 , 57.478 , 57.478, 38.551)
lng <- c(-10.854, -10.854, -10.854, -10.854, -11.655, -11.655, 2.021 , 2.021 , 2.021, 5.256)
type <- c("A","C","B","B","C","A","B","A","C","B")
date <- c(152.5,307.5,145,481,152,109.5,258.5,107.5,186.5,150)
start <- c(123,235,135,192,149,101,205,75,155,100)
stop <- c(182,380,155,289,155,218,312,140,218,200)
myData <- data.frame(id,type,date,start,stop,lat,lng)


chronogramme<- function(dataId){

  dataFiltered<-filter(myData,id==dataId)

  p<- ggplot(dataFiltered,aes(type,date))+
    geom_linerange(aes(ymin=start,ymax=stop),size=5)+
    coord_flip()
  return(p)
}


ui <- fluidPage(
  leafletOutput("map"),
  plotOutput("plot")
)


server <- function(input, output, session) {

  #Sortie map
  output$map <- renderLeaflet({
    leaflet()%>%
      addProviderTiles(providers$CartoDB.Positron) %>% 
      addCircleMarkers(
        layerId=~id,
        data = myData,
        lat = myData$lat,
        lng = myData$lng,
        radius = 5,
        color = 'blue',
        stroke = FALSE,
        fillOpacity = 1,
        group = 'markers'
      )
  })

  observeEvent(input$map_marker_click,{
    p <- chronogramme(input$map_marker_click$id)
    isolate({
      leafletProxy("map") %>% addPopupGraphs(list(p), group = 'markers')
    })
  })

}

# Create Shiny app ----
shinyApp(ui = ui, server = server)

如何访问对象的成员变量的解引用值

2 个答案: