即使在 C++ 中的 int main 之前声明函数后，函数也未在范围内声明

Question

我创建了两个向量，x_list和y_list。我在 int main 之前声明了两个函数，名为 x_i 和 y_j，它们用于在调用值之前提取元素一。例如，如果 x_i(2) 被称为 x_list[1]，则 y_j 的答案相同。我已经阅读了一些关于这个问题的答案，说变量应该在范围内，但我可以在我的代码中找到那个问题。

#include<iostream>
#include<iomanip>
#include <math.h>
#include <vector>
#include <algorithm>
using namespace std;

void display(vector<double> &v){
    for (int i = 0; i < v.size(); i++)
    {
        cout<<v[i]<<" ";
    }
    cout<<endl;
}
//-------------------------------
double x_i(int node_number)
{
    x_list[node_number-1];
}
//------------------------------
double y_j(int node_number)
{
    y_list[node_number-1];
}
//-----------------------------
int main(){

    const int N = 401;
    const double pi = 3.141592653589793;
    double L = pi/2;
    double r = 1.5;
    //-------------------------------------------------------------------
    vector<double> x_list_0_to_pidiv2;
    double val;
    for (int i = 0; i < (int(N/4)+1); i++)
    {
        val = ((L/2)*((1-(tanh(r*(1-(2*((i*(1))/int(N/4)))))/(tanh(r))))));
        x_list_0_to_pidiv2.push_back(val);   
    }
    //---------------------------------------------------------------------
    vector<double> dx_list;
    double diff;
    for (int i = 0; i < (((x_list_0_to_pidiv2).size())-1); i++)
    {
        diff = x_list_0_to_pidiv2[i+1]-x_list_0_to_pidiv2[i];
        dx_list.push_back(diff);
    }
    //----------------------------------------------------------------------
    // reversing the dx_list
    reverse(dx_list.begin(), dx_list.end());
    //----------------------------------------------------------------------
    vector<double> x_list;
    double entry1,entry2;
    for (int i = 0; i < ((x_list_0_to_pidiv2).size()); i++)
    {
        entry1 = x_list_0_to_pidiv2[i];
        x_list.push_back(entry1);
    }
    for (int k = 0; k < (dx_list.size()); k++)// equi to line 28 py
    {
        entry2 = x_list[k+(dx_list.size())] + dx_list[k];
        x_list.push_back(entry2);
    }
    //----------------------------------------------------------------------
    vector<double> dx_final_list;
    double diff2,val2;
    for (int i = 0; i < (x_list.size()-1); i++)
    {
        diff2 = x_list[i+1] - x_list[i];
        dx_final_list.push_back(diff2);
    }
    for (int i = 0; i <(dx_final_list.size()); i++)
    {
        val2 = x_list[i+dx_final_list.size()] + dx_final_list[i];
        x_list.push_back(val2);
    }
    //----------------------------------------------------------------------
    vector<double> y_list;
    double val3;
    for (int i = 0; i < x_list.size(); i++)
    {
        val3 = x_list[i];
        y_list.push_back(val3);
    }

错误如下：

trialc++.cpp: In function 'double x_i(int)':
trialc++.cpp:20:5: error: 'x_list' was not declared in this scope
     x_list[node_number-1];
     ^~~~~~
trialc++.cpp: In function 'double y_j(int)':
trialc++.cpp:25:5: error: 'y_list' was not declared in this scope
     y_list[node_number-1];
     ^~~~~~

注意：List是为了同名而写的，数据类型到处都是vector 非常感谢任何帮助！！

Answer 1

x_list 和 y_list 是 main() 内部的局部变量，因此它们超出了 x_i() 和 y_j() 中代码的范围。您必须将变量作为额外参数传递给这些函数，就像您使用 display() 一样，例如：

double x_i(const vector<double> &x_list, int node_number)
{
    return x_list[node_number-1];
}

double y_j(const vector<double> &y_list, int node_number)
{
    return y_list[node_number-1];
}

...

int main(){
    ...
    vector<double> x_list;
    vector<double> y_list;
    double d;
    ...
    d = x_i(x_list, some_node_number);
    ...
    d = y_j(y_list, some_node_number);
    ...
}

即使在 C++ 中的 int main 之前声明函数后，函数也未在范围内声明

Function not declared in scope even after declaring it before int main in C++

c++

scope

function

vector

stdvector