30

我正在尝试创建一个映射,其中键是 an int,值是一个数组,如下所示:

int red[3]   = {1,0,0};
int green[3] = {0,1,0};
int blue[3]  = {0,0,1};

std::map<int, int[3]> colours;

colours.insert(std::pair<int,int[3]>(GLUT_LEFT_BUTTON,red));    // THIS IS LINE 24!
colours.insert(std::pair<int,int[3]>(GLUT_MIDDLE_BUTTON,blue));
colours.insert(std::pair<int,int[3]>(GLUT_RIGHT_BUTTON,green));

但是,当我尝试编译此代码时,出现以下错误:

g++ (Ubuntu 4.4.1-4ubuntu8) 4.4.1

In file included from /usr/include/c++/4.4/bits/stl_algobase.h:66,
                 from /usr/include/c++/4.4/bits/stl_tree.h:62,
                 from /usr/include/c++/4.4/map:60,
                 from ../src/utils.cpp:9:
/usr/include/c++/4.4/bits/stl_pair.h: In constructor ‘std::pair<_T1, _T2>::pair(const _T1&, const _T2&) [with _T1 = int, _T2 = int [3]]’:
../src/utils.cpp:24:   instantiated from here
/usr/include/c++/4.4/bits/stl_pair.h:84: error: array used as initializer
/usr/include/c++/4.4/bits/stl_pair.h: In constructor ‘std::pair<_T1, _T2>::pair(const std::pair<_U1, _U2>&) [with _U1 = int, _U2 = int [3], _T1 = const int, _T2 = int [3]]’:
../src/utils.cpp:24:   instantiated from here
/usr/include/c++/4.4/bits/stl_pair.h:101: error: array used as initializer
In file included from /usr/include/c++/4.4/map:61,
                 from ../src/utils.cpp:9:
/usr/include/c++/4.4/bits/stl_map.h: In member function ‘_Tp& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const _Key&) [with _Key = int, _Tp = int [3], _Compare = std::less<int>, _Alloc = std::allocator<std::pair<const int, int [3]> >]’:
../src/utils.cpp:30:   instantiated from here
/usr/include/c++/4.4/bits/stl_map.h:450: error: conversion from ‘int’ to non-scalar type ‘int [3]’ requested
make: *** [src/utils.o] Error 1

我真的看不出错误在哪里。或者即使有错误。

4

9 回答 9

44

你不能像这样按值复制数组。

这里有几个解决方案,但我推荐#4以满足您的需求:

  1. 使用 anstd::vector而不是数组。

  2. 使用指向 3 个元素数组的指针映射:

    int red[3]   = {1,0,0};
    int green[3] = {0,1,0};
    int blue[3]  = {0,0,1};
    std::map<int,int(*)[3]> colours;
    colours.insert(std::pair<int,int(*)[3]>(GLUT_LEFT_BUTTON,&red));
    colours.insert(std::pair<int,int(*)[3]>(GLUT_MIDDLE_BUTTON,&blue));
    colours.insert(std::pair<int,int(*)[3]>(GLUT_RIGHT_BUTTON,&green));
    // Watch out for scope here, you may need to create the arrays on the heap.
    
  3. 使用boost 元组而不是 3 个元素的数组。

  4. 不要使用数组,而是创建一个包含 3 个元素的新结构。使map<int, newstructtype>. 或者将您的数组包装在一个结构中,如下所示:

    struct Triple
    {
        int color[3];
    };
    
    // Later in code
    Triple red = {1, 0, 0}, green = {0, 1, 0}, blue = {0, 0, 1};
    std::map<int,Triple> colours;
    colours.insert(std::pair<int,Triple>(GLUT_LEFT_BUTTON,red));
    colours.insert(std::pair<int,Triple>(GLUT_MIDDLE_BUTTON,blue));
    colours.insert(std::pair<int,Triple>(GLUT_RIGHT_BUTTON,green));
    
于 2010-04-06T03:45:35.710 回答
9

使用std::tr1::array

typedef std::tr1::array<int, 3> Triple;
Triple red   = {1, 0, 0};
Triple green = {0, 1, 0};
Triple blue  = {0, 0, 1};
std::map<int, Triple> colours;
colours.insert(std::make_pair(GLUT_LEFT_BUTTON,   red));
colours.insert(std::make_pair(GLUT_MIDDLE_BUTTON, blue));
colours.insert(std::make_pair(GLUT_RIGHT_BUTTON,  green));

std::array在 C++11 及更高版本中

using  Triple = std::array<int, 3>; 
Triple red   = {1, 0, 0};
Triple green = {0, 1, 0};
Triple blue  = {0, 0, 1};
std::map<int, Triple> colours;
colours.insert(std::make_pair(GLUT_LEFT_BUTTON,   red));
colours.insert(std::make_pair(GLUT_MIDDLE_BUTTON, blue));
colours.insert(std::make_pair(GLUT_RIGHT_BUTTON,  green));
于 2010-04-06T06:15:37.453 回答
8

数组不是 C++ 中的第一类构造。它们不是Copy Constructible,也不Assignable是对 的值的要求std::map。您可以使用boost::arraystd::vector

于 2010-04-06T03:49:59.063 回答
6

不要映射到 int[],而是像这样映射到 int*:

#include <iostream>
#include <map>
using namespace std;
int main(){
    std::map<int,int*> colors;
    int red[] = {3,7,9};
    colors[52] = red;
    cout << colors[52][1];  //prints 7
    colors[52][1] = 11;
    cout << colors[52][1];  //prints 11
    return 0;
}
于 2012-05-31T16:56:44.480 回答
3

另一种选择是将数组放在包装结构中:

    struct Wrapper { int value[3]; };

    // ...
    Wrapper red = {{1,0,0}};    
    std::map<int,Wrapper> colours;    
    colours.insert(std::pair<int,Wrapper>(1, red));
于 2010-04-06T03:55:05.227 回答
1

数组不能是标准容器中的存储数据( std::pair)

于 2010-04-06T03:50:37.410 回答
0

在 C++ 中使用结构的方法

int MAX_DATA_PER_INSTR = 8;
//struct to hold the values. remember to write the constructor
struct InstrChar
{
  InstrChar(int in[MAX_DATA_PER_INSTR]) { 
    //c alternative is memcopy
    std::copy(in, in+MAX_DATA_PER_INSTR, data);
  }
  int data[MAX_DATA_PER_INSTR];
};

// create a key value pair 
std::map <int, InstrChar> address_instructions;
std::map <int, InstrChar>::iterator it;

// sample array, 8 elements
int xp[MAX_DATA_PER_INSTR ] = {31,4,3,4,4,3,1,2};
address_instructions.insert(std::pair<int, InstrChar>(PC, xp));
it = address_instructions.find(PC);
InstrChar buf1 = it->second;
//integer pointer to the array, can be dereferenced as *p, *(p+1), ....    //*(p+7)
int *p = buf1.data;

//in case you need to print these values out. They can also be referred to as buf1.data[0], buf1.data[1], buf1.data[2]
printf("%d\n", (*p));
printf("%d\n", *(p+1));
printf("%d\n", *(p+2));
printf("%d\n", *(p+3));
printf("%d\n", *(p+4));
printf("%d\n", *(p+5));
printf("%d\n", *(p+6));
printf("%d\n", *(p+7));
于 2017-10-03T22:11:26.230 回答
0

我想扩展Brian R. Bondy 回答的第三项:自C++11以来,类模板std::tuple可用。所以你不再需要 Boost 来处理元组。

元组是可以容纳多个元素的固定大小的集合。与eg相比,std::vector它具有可以存储异构类型的优势。例如,如果要将颜色名称与其 RGB 值一起存储,则可以将std::string颜色名称的第四个类型元素添加到元组中。但是对于您的特定用例,代码可以编写如下:

int main() {
    using col_t = std::tuple<int, int, int>;
    col_t red   = { 1, 0, 0 };
    col_t green = { 0, 1, 0 };
    col_t blue  = { 0, 0, 1 };

    std::map<int, col_t> colours;

    colours.emplace(GLUT_LEFT_BUTTON, red);
    colours.emplace(GLUT_MIDDLE_BUTTON, blue);
    colours.emplace(GLUT_RIGHT_BUTTON, green);

    for (auto const &kv : colours)
        std::cout << kv.first << " => { " << std::get<0>(kv.second) << ", "
                                          << std::get<1>(kv.second) << ", "
                                          << std::get<2>(kv.second) << " }" << std::endl;
    return 0;
}

输出:

0 => { 1, 0, 0 }
1 => { 0, 0, 1 }
2 => { 0, 1, 0 }

注意:使用C++17使用元组变得更容易,尤其是如果您想同时访问多个元素。例如,如果您使用结构化绑定,您可以按如下方式打印元组:

for (auto const &[k, v] : colours) {
    auto [r, g, b] = v;
    std::cout << k << " => { " << r << ", " << g << ", " << b << " }" << std::endl;
}

Coliru 上的代码

于 2020-08-04T09:21:02.247 回答
0

如果要将数组传递给 C++ 中的 Map 函数。此代码可能会对您有所帮助。这将数组元素作为输入,并将其插入到具有出现次数的 map 函数中。 对于数组 {1, 2, 1, 2, 3, 4, 1} 映射将是 >> 元素:出现次数 1 3, 2 2. 3 1, 4 1

#include<bits/stdc++.h>

using namespace std;

int main()
{
    int size;
    cin>>size;
    int arr[size];
    for(int i = 0 ; i < size ; i++)
    {
        cin >> arr[i];
    }
    
    map <int,int> mp;
    for(int i = 0 ; i < size ;  i++)
        mp[arr[i]]++;
        
        for (auto i = mp.begin(); i != mp.end(); i++) 
        cout << i->first << "      " << i->second << endl; 
        
        return 0;
        //@rsMayank
}

希望它可以帮助你~ Mayank Srivastava

于 2021-02-03T10:26:47.413 回答