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定义类方法的错误总结

news 2025/6/20 6:01:21

struct Renderer
{vector<function<void(vector<string>)>> fileDropListeners;// 定义一个方法，它是将一个函数作为输入，callback是形参void print(function<void(float)> callback_func);void onFileDrop(function<void(vector<string>)> callback) {fileDropListeners.push_back(callback);}
};void print(function<void(float)> callback_func) {float a;std::cin >> a;callback_func(a);
}

出现错误：

Build started at 22:10...
1>------ Build started: Project: Project1, Configuration: Debug x64 ------
1>Source.cpp
1>Source.obj : error LNK2019: unresolved external symbol "public: void __cdecl Renderer::print(class std::function<void __cdecl(float)>)" (?print@Renderer@@QEAAXV?$function@$$A6AXM@Z@std@@@Z) referenced in function main
1>D:\work\VSsource\repos\cpplearn\Project1\x64\Debug\Project1.exe : fatal error LNK1120: 1 unresolved externals
1>Done building project "Project1.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
========== Build completed at 22:10 and took 00.793 seconds ==========

想要实现在结构体中仅声明方法，在结构体外进行定义，但是遇到连接错误。原因是下面定义的print并没有正确地定义给结构体中的print方法。而在main()函数中却使用了他。从而出现连接报错。正确修改应该是：在结构体外（外命名空间中）定义方法时一定要表明类对象：修改如下：

struct Renderer
{vector<function<void(vector<string>)>> fileDropListeners;// 定义一个方法，它是将一个函数作为输入，callback是形参void print(function<void(float)> callback_func);void onFileDrop(function<void(vector<string>)> callback) {fileDropListeners.push_back(callback);}
};void Renderer::print(function<void(float)> callback_func) {float a;std::cin >> a;callback_func(a);
}void lambda(float a) {printf("lambda hello %f!", a);
}