“未定义的参考"一个非常简单的c ++程序中的错误 [英] "undefined reference" error in a very very simple c++ program

问题描述

我有一个简单的程序，我完全从 http ://www.learncpp.com/cpp-tutorial/19-header-files/，因为我正在学习如何制作包含多个文件的c ++程序.

I have a simple program, which I copied exactly from the example in http://www.learncpp.com/cpp-tutorial/19-header-files/ because I'm learning how to make c++ programs with multiple files.

程序可以编译，但是在编译时会出现以下错误:

The program compiles but when building, the following error appears:

/tmp/ccm92rdR.o:在函数main中: main.cpp :(.text + 0x1a):对`add(int，int)'的未定义引用 collect2:ld返回1个退出状态

/tmp/ccm92rdR.o: In function main: main.cpp:(.text+0x1a): undefined reference to `add(int, int)' collect2: ld returned 1 exit status

代码如下:

main.cpp

#include <iostream>
#include "add.h" // this brings in the declaration for add()

int main()
{
    using namespace std;
    cout << "The sum of 3 and 4 is " << add(3, 4) << endl;
    return 0;
}

add.h

#ifndef ADD_H
#define ADD_H

int add(int x, int y); // function prototype for add.h

#endif

add.cpp

int add(int x, int y)
{
    return x + y;
}

有人知道为什么会这样吗?

Does anyone knows why this happens?

非常感谢您.

推荐答案

该代码几乎是完美的.

The code is almost perfect.

添加一行#include "add.h" in add.cpp`.

Add a line #include "add.h" inadd.cpp`.

将文件作为g++ main.cpp add.cpp一起编译，将生成可执行文件a.out

Compile the files together as g++ main.cpp add.cpp and it will produce an executablea.out

您可以将可执行文件作为./a.out运行，它将产生输出"3和4之和为7"(不带引号)

You can run the executable as ./a.out and it will produce the output "The sum of 3 and 4 is 7" (without the quotes)

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