c++ - 即使使用包含保护也会出现多个定义错误
问题描述
我的任务是在将代码分解为多个文件的同时保持循环依赖,代码是关于使用面向对象的台球模拟,但我的问题不是代码而是编译。
我已经解决了这个问题,并使用这篇文章解决了我的问题:Resolve build errors due to circular dependency between classes
但是在“make”命令之后我不断收到编译错误,说我已经多次定义了一些东西;这是当我使用包含保护来阻止程序多次包含定义时,我不知何故觉得我在某个地方犯了一个小错误,我似乎没有找到它。
这些是我的文件
球.cpp
#ifndef BALL_CPP
#define BALL_CPP
#include "ball.hpp"
#include <iostream>
using namespace std;
Ball::Ball(double _x, double _y, double _vx, double _vy, Table *t)
{
cout << "Ball constructor called" << endl;
table = t;
set_location(_x, _y);
set_speed(_vx, _vy);
cout << "Initial position is: (" << x << ',' << y << ')' << endl;
}
void Ball::set_location(double _x, double _y)
{
cout << "Ball::set_location called with (" << _x << ',' << _y << ')' << endl;
if (!table->contains_point(_x, _y))
abort();
x = _x;
y = _y;
}
void Ball::set_speed(double _vx, double _vy)
{
cout << "Ball::set_speed called with (" << _vx << ',' << _vy << ')' << endl;
vx = _vx;
vy = _vy;
}
void Ball::move(double dt)
{
cout << "Ball::move called" << endl;
x += vx * dt;
y += vy * dt;
if (!table->contains_point(x, y))
table->reflect(this);
cout << "New position is: (" << x << ',' << y << ')' << endl;
}
#endif
球.hpp
#ifndef BALL_HPP
#define BALL_HPP
#include "table.hpp"
class Ball
{
public:
Ball(double _x, double _y, double _vx, double _vy, Table *t);
void move(double dt);
double get_x() { return x; }
double get_y() { return y; }
double get_vx() { return vx; }
double get_vy() { return vy; }
void set_location(double _x, double _y);
void set_speed(double _vx, double _vy);
private:
double x;
double y;
double vx;
double vy;
Table *table;
};
#endif
表.cpp:
#ifndef TABLE1CPP
#define TABLE1CPP
using namespace std;
#include <iostream>
#include "ball.hpp"
Table::Table(double w, double h)
{
cout << "Table constructor called" << endl;
if (w <= 0 || h <= 0)
abort();
width = w;
height = h;
}
bool Table::contains_point(double x, double y)
{
cout << "Table::contains_point called" << endl;
return x >= 0 && x < width && y >= 0 && y < height;
}
void Table::reflect(Ball *b)
{
cout << "Table::reflect called" << endl;
double x = b->get_x();
double y = b->get_y();
double vx = b->get_vx();
double vy = b->get_vy();
while (!contains_point(x, y))
{
if (x < 0)
{
x = -x;
vx = -vx;
}
if (x >= width)
{
x = 2 * width - x;
vx = -vx;
}
if (y < 0)
{
y = -y;
vy = -vy;
}
if (y >= height)
{
y = 2 * height - y;
vy = -vy;
}
}
b->set_location(x, y);
b->set_speed(vx, vy);
}
#endif
表.hpp:
#ifndef TABLE_HPP
#define TABLE_HPP
class Ball;
class Table
{
public:
Table(double w, double h);
bool contains_point(double x, double y);
void reflect(Ball *b);
private:
double width;
double height;
};
#endif
我的makefile看起来像这样:(我对多文件概念非常陌生,而且非常缺乏经验,所以我在这里可能有一个我不明白的错误)
生成文件:
output: main.o table.o ball.o
g++ main.o ball.o table.o -o billiards
main.o: main.cpp
g++ -c main.cpp
ball1.o: ball.cpp ball.hpp
g++ -c ball1.cpp
table1.o: table.cpp table.hpp
g++ -c table.cpp
clean:
rm * .o output
主.cpp:
#include <iostream>
#include <cstdlib>
#include "ball.cpp" // should be changed to "ball.hpp"
#include "table.cpp" // should be changed to "table.hpp"
using namespace std;
int main()
{
Table t(100, 50);
Ball b(10, 20, 25, 5, &t);
b.move(10);
}
错误:
/usr/bin/ld: ball.o: in function `Ball::Ball(double, double, double, double, Table*)':
ball.cpp:(.text+0x0): multiple definition of `Ball::Ball(double, double, double, double, Table*)'; main.o:main.cpp:(.text+0x0): first defined here
/usr/bin/ld: ball.o: in function `Ball::set_location(double, double)':
ball.cpp:(.text+0x10c): multiple definition of `Ball::set_location(double, double)'; main.o:main.cpp:(.text+0x10c): first defined here
/usr/bin/ld: ball.o: in function `Ball::set_speed(double, double)':
ball.cpp:(.text+0x1dc): multiple definition of `Ball::set_speed(double, double)'; main.o:main.cpp:(.text+0x1dc): first defined here
/usr/bin/ld: ball.o: in function `Ball::Ball(double, double, double, double, Table*)':
ball.cpp:(.text+0x0): multiple definition of `Ball::Ball(double, double, double, double, Table*)'; main.o:main.cpp:(.text+0x0): first defined here
/usr/bin/ld: ball.o: in function `Ball::move(double)':
ball.cpp:(.text+0x280): multiple definition of `Ball::move(double)'; main.o:main.cpp:(.text+0x280): first defined here
/usr/bin/ld: table.o: in function `Table::Table(double, double)':
table.cpp:(.text+0x0): multiple definition of `Table::Table(double, double)'; main.o:main.cpp:(.text+0x3be): first defined here
/usr/bin/ld: table.o: in function `Table::Table(double, double)':
table.cpp:(.text+0x0): multiple definition of `Table::Table(double, double)'; main.o:main.cpp:(.text+0x3be): first defined here
/usr/bin/ld: table.o: in function `Table::contains_point(double, double)':
table.cpp:(.text+0x7c): multiple definition of `Table::contains_point(double, double)'; main.o:main.cpp:(.text+0x43a): first defined here
/usr/bin/ld: table.o: in function `Table::reflect(Ball*)':
table.cpp:(.text+0x10a): multiple definition of `Table::reflect(Ball*)'; main.o:main.cpp:(.text+0x4c8): first defined here
collect2: error: ld returned 1 exit status
make: *** [Makefile:2: output] Error 1
解决方案
好的,这就是正在发生的事情:main.cpp
正在拉取ball.cpp
and table.cpp
,因此目标文件将包含您在andmain.o
中实现的所有函数和变量的完整实现。这是一个问题,因为您还单独编译and ,因此您最终会得到所有重复项。ball.cpp
table.cpp
ball.cpp
table.cpp
我猜您将包含保护放在 .cpp 文件中以避免此问题,但是,这实际上不起作用:#define
'd 宏不会在编译器的调用之间结转。
您在这里要做的是#include
.hpp 文件:main.cpp
将能够看到您正在使用的功能的声明,但它不会将实现编译成main.o
,因此不会与ball.o
or发生任何冲突table.o
。此外,您可能应该从 .cpp 文件中删除包含保护:正是由于这些重复的原因,#include
通常不会执行 C 或 C++ 源文件,除非在一些与您的特定情况无关的奇怪情况下.
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