C++ 错误：对“main”的未定义引用
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C++ Error: undefined reference to `main'
提问by smileham
I'm working on a simple class List, but when compiling the header and cpp file, I get the error: undefined reference to `main'
我正在处理一个简单的类 List，但是在编译头文件和 cpp 文件时，出现错误：未定义对 `main' 的引用
What am I doing wrong, and how could I fix this?
我做错了什么，我该如何解决？
Here is the list.h file that has simple headers:
这是具有简单标题的 list.h 文件：
list.h
列表.h
#ifndef LIST_H
#define LIST_H
#include <string>
const int DEFAULT_CAPACITY = 100;
class List
{
public:
List();
List(int capacity);
~List();
void push_back(std::string s);
int size() const;
std::string at(int index) const;
private:
std::string* mData;
int mSize;
int mCapacity;
};
#endif
And here is the list.cpp file:
这是 list.cpp 文件：
list.cpp
列表.cpp
#include "list.h"
#include <string>
List::List(){
mData = new std::string[DEFAULT_CAPACITY];
mSize = 0;
mCapacity = 100;
};
List::List(int capacity){
mData = new std::string[capacity];
mSize = 0;
mCapacity = capacity;
};
List::~List(){
delete[] mData;
};
void List::push_back(std::string s){
if (mSize<mCapacity){
mData[mSize] = s;
mSize++;
}
};
int List::size() const{
return mSize;
};
std::string List::at(int index) const{
return mData[index];
};
I tried experimenting around with "using namespace std" and how to include , but I can't figure out how to get these errors to go away. What is causing them?
我尝试尝试使用“使用命名空间 std”以及如何包含，但我不知道如何消除这些错误。是什么导致了它们？
采纳答案by Lundin
Undefined reference to main() means that your program lacks a main() function, which is mandatory for all C++ programs. Add this somewhere:
对 main() 的未定义引用意味着您的程序缺少 main() 函数，这对于所有 C++ 程序都是必需的。在某处添加这个：
int main()
{
return 0;
}
回答by Keith Thompson
You should be able to compilelist.cpp, you can't linkit unless you have a main program. (That might be a slight oversimplification.)
你应该能够编译list.cpp，除非你有一个主程序，否则你不能链接它。（这可能有点过于简单化了。）
The way to compile a source file without linking it depends on what compiler you're using. If you're using g++, the command would be:
在不链接的情况下编译源文件的方法取决于您使用的编译器。如果您正在使用g++，命令将是：
g++ -c list.cpp
That will generate an object file containing the machine code for your class. Depending on your compiler and OS, it might be called list.oor list.obj.
这将生成一个包含您的类的机器代码的目标文件。根据您的编译器和操作系统，它可能被称为list.o或list.obj。
If you instead try:
如果您改为尝试：
g++ list.cpp
it will assume that you've defined a mainfunction and try to generate an executable, resulting in the error you've seen (because you haven'tdefined a mainfunction).
它将假设您已经定义了一个main函数并尝试生成一个可执行文件，从而导致您看到的错误（因为您还没有定义一个main函数）。
At some point, of course, you'll need a program that uses your class. To do that, you'll need another .cppsource file that has a #include "list.h"and a main()function. You can compile that source file and link the resulting object together with the object generated from list.cppto generate a working executable. With g++, you can do that in one step, for example:
当然，在某些时候，您将需要一个使用您的类的程序。为此，您需要另一个.cpp具有 a#include "list.h"和 amain()函数的源文件。您可以编译该源文件并将生成的对象与生成的对象链接在一起list.cpp以生成工作可执行文件。使用g++，您可以一步完成，例如：
g++ list.cpp main.cpp -o main
You have to have a mainfunction somewhere. It doesn't necessarily have to be in list.cpp. And as a matter of style and code organization, it probably shouldn't be in list.cpp; you might want to be able to use that class from more than one main program.
你必须在main某处有一个功能。它不一定必须在list.cpp. 作为风格和代码组织的问题，它可能不应该在list.cpp; 您可能希望能够从多个主程序中使用该类。
