C++:不能修改全局变量

Question

我现在正在处理一项任务，但在将数据组的新成员添加到链表时遇到了一些困难。我已经用谷歌搜索并查看了所有内容，但我一直无法找到解决问题的方法。问题是当我在 Openbutton_Click 中打开文件时，我全局声明的 6 个变量(客户和 5 个节点类型变量)最初被修改。但是我无法稍后在 addconf_Click 中修改变量。通常我不会发帖求助，但我时间不多了，想不通。我在格式化时遇到了很多问题，请耐心等待。

这是 myform.h 附带的 .cpp 文件

#include "MyForm.h"

using namespace System; 
using namespace System::Windows::Forms; 
using namespace std;

int customers = 0;
node *current;
node *first;
node *last;
node *temp;
node *previous;


[STAThread] 
void Main(array<String^>^ args) { 
Application::EnableVisualStyles(); 
Application::SetCompatibleTextRenderingDefault(false); 

Project1::MyForm form;

Application::Run(%form); 
}

这一切都在 myform.h 中

#pragma once
#include <fstream>
#include <string>
#include <iostream>
#include <sstream>
#include <msclr\marshal_cppstd.h>
#include "header.h"

using namespace std;

struct node{
account customer;
node *next;

};

extern int customers;
extern node *current;
extern node *first;
extern node *last;
extern node *temp;
extern node *previous;

private: System::Void Openbutton_Click(System::Object^  sender, System::EventArgs^  e) {
ifstream fin;

openFileDialog1->ShowDialog();

String^ filenname = System::IO::Path::GetFileName(openFileDialog1->FileName);
std::string filename = msclr::interop::marshal_as<std::string>(filenname);

fin.open(filename);


if (fin){
    this->label2->Text = "File Opened";
}
else
    this->label2->Text = "Failed to Open File";

String^ menu;
String^ temp;
string input;
string name;
string numstr;
string pinstr;
string balstr;
int num;
int pin;
float bal;

first = new node;

getline(fin, input);

numstr = input.substr(0, 3);

stringstream convert3(numstr);
convert3 >> num;


name = input.substr(8, 16);

name.erase(name.find_last_not_of(" \n\r\t") + 1);

pinstr = input.substr(24, 4);


balstr = input.substr(30, 7);



stringstream convert(pinstr);
convert >> pin;

stringstream convert2(balstr);
convert2 >> bal;

first->customer.setNum(num);
first->customer.setName(name);
first->customer.setPin(pin);
first->customer.setBal(bal);
first->next = 0;

numstr.clear();
name.clear();
pinstr.clear();
balstr.clear();

current = first;

customers++;

while (fin){
    customers++;
    previous = current;
    current->next = new node;
    current = current->next;

        getline(fin, input);

        numstr = input.substr(0, 3);

        name = input.substr(8, 16);

        name.erase(name.find_last_not_of(" \n\r\t") + 1);

        pinstr = input.substr(24, 4);

        balstr = input.substr(30, 7);

        stringstream convert3(numstr);
        convert3 >> num;

        stringstream convert(pinstr);
        convert >> pin;

        stringstream convert2(balstr);
        convert2 >> bal;


        current->customer.setNum(num);
        current->customer.setName(name);
        current->customer.setPin(pin);
        current->customer.setBal(bal);

    }
    last = previous;
    last->next = 0;
    customers--;
    cout << "All accounts loaded, system ready." << endl;
    // Print and fill the textbox
    current = first;

    menu = "Account List:" + customers + "\r\n " + "Num | Account Holder | Pin | Balance\r\n";


    for (int c = 0; c < customers; c++){
        menu += current->customer.getNum();
        menu += " | ";
        temp = gcnew String(current->customer.getName().c_str());
        menu += temp;
        menu += " | ";
        menu += current->customer.getPin();
        menu += " | $";
        menu += current->customer.getBal();
        menu += "\r\n";

        if (current->next != 0){
            current = current->next;
        }
        else
            c = customers;
    }


textBox1->Text = gcnew String(menu);
launch->Visible = true;
addCust->Visible = true;
remCust->Visible = true;
refList->Visible = true;
}

private: System::Void addconf_Click(System::Object^  sender, System::EventArgs^  e) {
int num = -1;
string name = "";
int pin = -1;
float bal = -1;
bool match = false;

string numstr = msclr::interop::marshal_as<std::string>(addnumbox->Text);
num = stoi(numstr);
name = msclr::interop::marshal_as<std::string>(addnamebox->Text);


name.erase(name.find_last_not_of(" \n\r\t") + 1);
string pinstr = msclr::interop::marshal_as<std::string>(addpinbox->Text);
pin = atoi(pinstr.c_str());

string balstr = msclr::interop::marshal_as<std::string>(addbalbox->Text);
bal = stof(balstr);

if (num != -1 && pin != -1 && name != "" && bal != -1){

    current = new node;
    last->next = current;
    current->customer.setNum(num);
    current->customer.setName(name);
    current->customer.setPin(pin);
    current->customer.setBal(bal);
    current->next = 0;


    last = current;
    customers = customers + 1;
    num = -1;
    pin = -1;
    name = "";
    bal = -1;


    }


}

header.h在这里

#include <string>
#include <iostream>

using namespace std;


class account{
private:
int accNum;
int accPin;
string accName;
float accBal;

public:
void setNum(int num);
void setPin(int pin);
void setName(string name);
void setBal(float bal);
void deposit(float money);
void withdraw(float money);

int getNum();
int getPin();
string getName();
float getBal();
};

void account::setNum(int num){
accNum = num;
}

void account::setPin(int pin){
accPin = pin;
}

void account::setName(string name){
accName = name;
}

void account::setBal(float bal){
accBal = bal;
}

int account::getNum(){
return accNum;
}

int account::getPin(){
return accPin;
}

string account::getName(){
return accName;
}

float account::getBal(){
return accBal;
}

void account::deposit(float money){
accBal = accBal + money;
}

void account::withdraw(float money){
accBal = accBal - money;
}

Answer 1

您在头文件中将 customers 声明为一个 int。请记住，头文件是直接粘贴到包含它的文件中的。因此您将有许多该变量的实例。

正确的做法是在 cpp 文件中定义它，并通过在头文件中使用 extern int customers 使其成为全局的。

同样的问题也适用于您的节点-变量。您必须在 cpp 文件中定义它们，以便它们只存在于一个地方。

但是，像这样使用全局可变变量几乎不是一个好主意。