[英]Class object is 'undefined' in int main()
I have two .cpp files "rational.cpp" and "main.cpp" and one "rational.h" file. 我有两个.cpp文件“ rational.cpp”和“ main.cpp”,以及一个“ rational.h”文件。 In "rational.cpp" I have a declared a Rational class, and included "rational.h" at the top of both files;
在“ rational.cpp”中,我声明了一个Rational类,并且在两个文件的顶部都包含了“ rational.h”。 however when I try to create the object
Rational rat;
但是,当我尝试创建对象
Rational rat;
. 。 I get the error 'identifier "Rational" is undefined'.
我收到错误“标识符“ Rational”未定义”。 I am very confused.
我很困扰。
Here is "main.cpp" 这是“ main.cpp”
#include "rational.h"
int main() {
int select = 1, n, d;
while (select != 0) {
cout << "Enter numerator";
cin >> n;
cout << "\nEnter denominator";
cin >> d;
try {
if (d == 0) {
throw 0;
}
}
catch (int e) {
cout << "/nerror: cannot divide by 0" << endl;
cout << "enter a new denominator: ";
cin >> d;
}
Rational rat;
cout << "1. Add a rational\n2. Subtract a rational\n3. Multiply by a rational\n4. Divide by a rational\n0. Exit";
cout << "enter selector" << endl;
cin >> select;
switch (select) {
case 1: rat.add(n, d); break;
case 2: rat.sub(n, d); break;
case 3: rat.mul(n, d); break;
case 4: rat.div(n, d); break;
case 0: break;
default:
try {
throw select;
}
catch (int e) {
cout << e << " is not a valid option" << endl;
}
catch (...) {
cout << "error: invalid option" << endl;
}
break;
}
}
return 0;
}
"rational.cpp" “ rational.cpp”
#include "rational.h"
class Rational{
public:
void reduce(int n, int d);
//define math functions
void add(int n, int d);
void sub(int n, int d);
void div(int n, int d);
void mul(int n, int d);
};
void Rational::reduce(int n, int d) {
}
void Rational::add(int n, int d) {
}
void Rational::sub(int n, int d) {
}
void Rational::div(int n, int d) {
}
void Rational::mul(int n, int d) {
}
"rational.h" “ rational.h”
#pragma once
#ifndef RATIONAL
#define RATIONAL
#include <iostream>
#include <math.h>
#include <exception>
using namespace std;
#endif
and my Makefile 和我的Makefile
rational.exe: main.o rational.o
g++ -o rational.exe main.o rational.o
main.o: main.cpp rational.h
g++ -c main.cpp
rational.o: rational.cpp rational.h
g++ -c rational.cpp
I am using cygwin to compile. 我正在使用cygwin进行编译。
The declaration of rational
has to be inside the header, or else the compiler won't read it (for lack of a better word) in main.cpp. rational
的声明必须在标头中,否则编译器将不会在main.cpp中读取它(因为缺少更好的词)。
You need to move the declaration (ie the following portion) to rational.h: 您需要将声明(即以下部分)移至Rational.h:
class Rational{
public:
void reduce(int n, int d);
//define math functions
void add(int n, int d);
void sub(int n, int d);
void div(int n, int d);
void mul(int n, int d);
};
For more information, see this question . 有关更多信息,请参见此问题 。
Although you included Rational.h in you main.cpp file, Rational.h doesn't contain any definition/declaration of the Rational class. 尽管您在main.cpp文件中包括了Rational.h,但是Rational.h不包含Rational类的任何定义/声明。 declare / define the Rational class in the Rational.h file and keep all the functions implementation in you cpp file.
在Rational.h文件中声明/定义Rational类,并将所有函数实现保留在cpp文件中。 Add
加
class Rational;
to you header file 给你头文件
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