英文:
has initializer but incomplete type (stuct c++)
问题
I don't understand what's going on
#ifndef __UTIL__
#define __UTIL__
struct Contact;
using Contact = struct Contact;
#endif
#include "util.hpp"
#include <iostream>
struct Contact
{
std::string fistname;
std::string lastname;
int age;
std::string number;
};
#include "util.hpp"
#include <iostream>
int main()
{
Contact newContact{"Cage", "Jhonny", 20, "+33225254554"};
return 0;
}
Compilation result:
I don't understand why there is this error. But everything seems correct.
英文:
I don't understand what's going on
Util.hpp>>>>>>>>>>
#ifndef __UTIL__
#define __UTIL__
struct Contact;
using Contact = struct Contact;
#endif
Util.cpp>>>>>>>>>
#include "util.hpp"
#include <iostream>
struct Contact
{
std::string fistname;
std::string lastname;
int age;
std::string number;
};
main.cpp>>>>>>>>>>>
#include "util.hpp"
#include <iostream>
int main()
{
Contact newContact{"Cage", "Jhonny", 20 ,"+33225254554"};
return 0;
}
compilation result >>>>>>>>>>>>
I don't understand why there is this error. But everything seems correct
答案1
得分: 2
你必须将整个struct定义放在你的util.hpp文件中。你现在只有对在main.cpp看来从未被完整解释的某事的前向声明。
在编译器术语中，这是一种“不完整类型”。
英文:
You must put your entire struct definition in your util.hpp file. All you have now is a forward declaration to something that as far as main.cpp is concerned, is never fully explained.
In compiler terms, this is an "incomplete type".
答案2
得分: 0
Contact在main.cpp中是一个不完整的类型。
在util.hpp中像struct Contact这样的声明被称为前向声明：你基本上告诉编译器将来会定义一个名为Contact的结构体。只有前向声明，你只能声明指向Contact的指针和/或引用，因为编译器不需要知道它的大小来处理指针和引用。
但是要在main.cpp中实际声明一个类型为Contact的变量，编译器需要一个完整的类型，而不仅仅是将来会存在的东西的名称 —— 它需要知道它是什么。通常情况下，你会在util.hpp中完全声明结构体，除非你有充分的理由不这样做。
英文:
Contact is an incomplete type in main.cpp.
A declaration like struct Contact in util.hpp is called a forward declaration: you are basically telling the compiler that a struct called Contact will eventually be defined. With just the forward declaration, you can only declare pointers and/or references to Contact, since the compiler does not need to know its size for pointers and references.
But to actually declare a variable of type Contact, in your main.cpp, the compiler needs a complete type, not just the name of something that will eventually exist -- it needs to know what it is. Typically you would fully declare the struct in Util.hpp unless you have a good reason not to.
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