未定义的函数引用 (c++)

Question

我问这个问题之前搜索了一下，我发现每个人都在使用 .h 文件来实现他们的功能，而我的老师教我们将 main 和功能放在一个文件中。

我只是想弄清楚为什么它是未定义的。我知道这段代码中可能还存在其他问题，但我真的无法弄清楚我做错了什么。

这是我的代码：

#include <iostream>
#include <iomanip>

using namespace std;

void start();
void process();
void check();
void deposit();

const float dserv = 0.10;
const float cserv = 0.15;
const float fiveserv = 5.0;
const float oserv = 10.0;

int main()
{
float balance;
float amount;
bool fivehun;
bool endcheck;
float servcharge;
float servchargetotal;
char type;

start();
while(endcheck != true)
{process();}
cout<<"Current balance: $"<<balance<<endl;
cout<<"Total service charges: $"<<servchargetotal<<endl;
cout<<"Final balance: $"<<
system("pause");
return 0;
}

void start(float balance)
{
    balance = 0;
    cout<<fixed<<showpoint<<setprecision(2);
    cout<<"Transactions will take the form of a letter followed by a dollar ";
    cout<<"amount. Valid letters are “C” for a check, “D” for a deposit, and";
    cout<<"“E” for the ending transaction (use zero on this transaction).";
    cout<<"Press <Enter> after each line of input";
    cout<<"Enter the beginning balance:"<<endl;
    cin>>balance;
}

void process(float balance, float amount, char type, bool endcheck)
{
    cout<<"Enter a transaction:"<<endl;
    cin>>type>>amount;
    if (type = "C"||"c")
    {check();
    endcheck = false;}
    else if(type = "D"||"d")
    {deposit();
    endcheck = false;}
    else if(type= "E"||"e")
    {endcheck = true;}
}

void check(float balance, float amount, bool fivehun, float servcharge, float& servchargetotal)
{
    balance = balance - amount;
    servcharge = cserv;
    if (balance<500.00)
    {fivehun = true;}
    else
    {fivehun = false;}

    cout<<"Transaction: Check in amount of $"<<amount<<endl;
    cout<<"Current balance: $"<<balance<<endl;
    cout<<"Service charge: Check - $"<<cserv<<endl;
    if (fivehun == true)
    {cout<<"Service charge: Below 0 - $"<<fiveserv<<endl;
     servcharge = (fiveserv+servcharge);}
    cout<<"Total service charges: $"<<servcharge<<endl;
    servchargetotal = servchargetotal + servcharge;
}

void deposit(float balance, float amount, bool fivehun, float servcharge, float& servchargetotal)
{
    balance = balance + amount;
    servcharge = dserv;
    if (balance<500.00)
    {fivehun = true;}
    else
    {fivehun = false;}

    cout<<"Transaction: Deposit in amount of $"<<amount<<endl;
    cout<<"Current balance: $"<<balance<<endl;
    cout<<"Service charge: Check - $"<<cserv<<endl;
    if (fivehun == true)
    {cout<<"Service charge: Below 0 - $"<<fiveserv<<endl;
     servcharge = (fiveserv+cserv);}
    cout<<"Total service charges: $"<<servcharge<<endl;
    servchargetotal = servchargetotal + servcharge;
}

如果有什么可以详细说明的地方，我会尽力edit/comment。

Answer 1

你声明了一个函数void start();。你用 start(); .

来称呼它

但是您从未为此函数提供函数体。您定义为 void start(float balance) 的函数是一个 不同的函数 。在 C++ 中，可能有多个具有相同名称但参数列表不同的函数；这些是不同的功能。

您在 process() 等方面也有类似的问题。

您的函数应该传递和返回它们使用的变量，但您实际上并没有编写函数来执行此操作。 void start(float balance) 中的 balance 与 main() 中的 float balance 是不同的变量；您在此函数中所做的更改不会影响 main.

中的 float balance;

要修复此特定功能，应该是：

float start();

在原型和函数定义中；你应该在函数内部有 float balance;，然后以 return balance; 结束。然后你像这样调用 main：balance = start();

您的课程材料应该涵盖将值传递给函数和从函数返回值，您需要参考它们来修复您的其他函数。

Answer 2

您定义了以下函数：

void start();
void process();
void check();
void deposit();

你实现了：

void start(float balance)
void process(float balance, float amount, char type, bool endcheck)
void check(float balance, float amount, bool fivehun, float servcharge, float& servchargetotal)
void deposit(float balance, float amount, bool fivehun, float servcharge, float& servchargetotal)

定义必须与实现相匹配。

或者，如果将实现放在文件中首次使用（在 main 中）之前，则可以删除定义。

函数调用与定义相匹配，但是当编译器（实际上是链接器）寻找看起来像 void start() 的函数实现时，它找到 void start(float balance) 并得出结论，这些不是关闭的足够匹配。

Answer 3

请使用此代码。这对你有帮助。

#include <iostream>
#include <iomanip>

using namespace std;

void start(float balance);
void process(float balance, float amount, char type, bool endcheck);
void check(float balance, float amount, bool fivehun, float servcharge, float& servchargetotal);
void deposit(float balance, float amount, bool fivehun, float servcharge, float& servchargetotal);

const float dserv = 0.10;
const float cserv = 0.15;
const float fiveserv = 5.0;
const float oserv = 10.0;

int main()
{
float balance;
float amount;
bool fivehun;
bool endcheck;
float servcharge;
float servchargetotal;
char type;

start(balance);
while(endcheck != true)
{process(balance, amount, fivehun, servcharge, servchargetotal);}
cout<<"Current balance: $"<<balance<<endl;
cout<<"Total service charges: $"<<servchargetotal<<endl;
cout<<"Final balance: $"<<
system("pause");
return 0;
}

void start(float balance)
{
balance = 0;
cout<<fixed<<showpoint<<setprecision(2);
cout<<"Transactions will take the form of a letter followed by a dollar ";
cout<<"amount. Valid letters are “C” for a check, “D” for a deposit, and";
cout<<"“E” for the ending transaction (use zero on this transaction).";
cout<<"Press <Enter> after each line of input";
cout<<"Enter the beginning balance:"<<endl;
cin>>balance;
}

void process(float balance, float amount, char type, bool endcheck)
{
cout<<"Enter a transaction:"<<endl;
cin>>type>>amount;
if (type = "C"||"c")
{check(balance, amount, ...);
endcheck = false;}
else if(type = "D"||"d")
{deposit(balance, amount, ...);
endcheck = false;}
else if(type= "E"||"e")
{endcheck = true;}
}

void check(float balance, float amount, bool fivehun, float servcharge, float& servchargetotal)
{
balance = balance - amount;
servcharge = cserv;
if (balance<500.00)
{fivehun = true;}
else
{fivehun = false;}

cout<<"Transaction: Check in amount of $"<<amount<<endl;
cout<<"Current balance: $"<<balance<<endl;
cout<<"Service charge: Check - $"<<cserv<<endl;
if (fivehun == true)
{cout<<"Service charge: Below 0 - $"<<fiveserv<<endl;
 servcharge = (fiveserv+servcharge);}
cout<<"Total service charges: $"<<servcharge<<endl;
servchargetotal = servchargetotal + servcharge;
}

void deposit(float balance, float amount, bool fivehun, float servcharge, float& servchargetotal)
{
balance = balance + amount;
servcharge = dserv;
if (balance<500.00)
{fivehun = true;}
else
{fivehun = false;}

cout<<"Transaction: Deposit in amount of $"<<amount<<endl;
cout<<"Current balance: $"<<balance<<endl;
cout<<"Service charge: Check - $"<<cserv<<endl;
if (fivehun == true)
{cout<<"Service charge: Below 0 - $"<<fiveserv<<endl;
 servcharge = (fiveserv+cserv);}
cout<<"Total service charges: $"<<servcharge<<endl;
servchargetotal = servchargetotal + servcharge;
}

Answer 4

按照 M.M 检查您的 start 函数。你应该得到这样的东西：

float start() {
    // ...
    float balance;
    cin >> balance;
    return balance;
}


int main() {
    float n;
    n = start();
    // ...
    return 0;
}

并逐步检查所有函数，因为您在下一个 process 函数中遇到问题：在 if 语句中必须是比较运算符 if (type == "C" || type == "c") 而不是赋值 type = "C"||"c".

未定义的函数引用 (c++)

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