我正在做一个小项目,以提高我在C++中的OOP技能-该项目只是一个简单的书籍收藏,有点像家庭图书馆,在那里,书籍可以存储在虚拟书架中,分组到更大的书摊中,并有各自的名称等,每本书都有自己的ID,是一个正整数。我试图创建一个用户定义的类析构函数,我想把析构函数的实现移到一个源文件中,遵循规则,将超过一行长的实现从.hpp文件移动到.cpp文件,以帮助养成生成更好优化、更快代码的习惯(当然,在本例中,这没有帮助,但我只想找到解决所遇到问题的方法,而不是在未来苦苦挣扎(。
然而,当试图编译我的代码时,我得到了以下错误:
c:/mingw/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: CMakeFiles/bookshelf.dir/objects.a(bookshelf.cpp.obj): in function `void std::_Destroy<Book>(Book*)':
c:/mingw/include/c++/9.2.0/bits/stl_construct.h:98: undefined reference to `Book::~Book()'
collect2.exe: error: ld returned 1 exit status
make.exe[2]: *** [CMakeFiles/bookshelf.dir/build.make:101: bookshelf.exe] Error 1
make.exe[1]: *** [CMakeFiles/Makefile2:139: CMakeFiles/bookshelf.dir/all] Error 2
make.exe: *** [Makefile:111: all] Error 2
The terminal process "C:WINDOWSSystem32WindowsPowerShellv1.0powershell.exe -Command cmake --build Build" terminated with exit code: 1.
我使用Visual Studio代码,并使用MinGW64编译器编译我的代码,在Windows 11上工作,我的项目是用以下CMakeLists文件设置的:
cmake_minimum_required(VERSION 3.0.0)
project(Book VERSION 0.1.0)
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED True)
# include(GoogleTest)
# enable_testing()
add_executable(main main.cpp)
add_executable(book src/book.cpp include/bookshelf.hpp include/book.hpp include/types.hpp include/helpers.hpp)
add_executable(bookshelf src/bookshelf.cpp include/bookshelf.hpp)
# add_executable(library src/library.cpp include/library.hpp)
add_compile_options(-Werror -Wextra -Wall -Wconversion -Wpedantic -pedantic-errors -unused-variable)
set(CPACK_PROJECT_NAME ${PROJECT_NAME})
set(CPACK_PROJECT_VERSION ${PROJECT_VERSION})
include(CPack)
include_directories(
include
src
)
以下是头文件和源文件的代码:book.cpp
#include <cstdlib>
#include <iostream>
#include <set>
#include "book.hpp"
#include "helpers.hpp"
Book::~Book(){
ids.erase(book_id_);
freed_ids.insert(book_id_);
//@TODO: To be implemented - destroy the object, not only deal with the book's ID!
};
Book::Book(Title title, Author author) : title_(title), author_(author){
if(!freed_ids.empty()){
book_id_ = *(freed_ids.begin());
}
else if(freed_ids.empty() && !ids.empty()){
book_id_ = *(ids.end());
}
else{
book_id_ = 0;
}
ids.insert(book_id_);
};
int main(){
std::cout << "Hello, from book.cpp!" << std::endl;
return EXIT_SUCCESS;
}
book.hpp
#ifndef book
#define book
#include "types.hpp"
#include "helpers.hpp"
/*
Class represeting a book as en entry in a collection of books.
@param author_ Author of the book.
@param title_ Title of the book.
@param book_id_ ID of a book.
*/
class Book{
private:
Author author_;
Title title_;
BookID book_id_;
public:
Book(Title title, Author author);
/*Get the title of the book.
@TODO: To be moved into a new class Library*/
Title get_title() const {return title_;}
/*Get the author of the book.
@TODO: To be moved into a new class Library*/
Author get_author() const {return author_;}
/*Get the ID number of the book.
@TODO: To be moved into a new class Library*/
BookID get_id() const {return book_id_;}
~Book();
};
#endif
简单地将析构函数的主体移动到.hpp文件可以使代码编译得很好,但这并不能解决我的问题。.cpp文件中定义的构造函数工作得很好,我不明白析构函数不工作的原因。
提前感谢您的帮助!
附言:如果我的代码中有什么东西毫无意义,只是愚蠢,也可以告诉我,像这样的情报将不胜感激。
@user17732522我已经应用了你在下面的答案中建议我的更改,析构函数的问题现在没有发生,但我收到了错误,指出我用来存储ID和名称的std::set对象有多个定义,它们看起来像这样:
c:/mingw/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe:
CMakeFiles/main.dir/objects.a(bookshelf.cpp.obj):C:/Users/Darek/Desktop/projects/myLibrary/include/helpers.hpp:9: multiple definition of `ids';
CMakeFiles/main.dir/objects.a(book.cpp.obj):C:/Users/Darek/Desktop/projects/myLibrary/include/helpers.hpp:9: first defined here
除了引用freed_ids和shelf_name std::set类型对象之外,还有两个类似的错误。
这是helper.hpp文件,不是很复杂:
#ifndef HELPERS_HEADER_GUARD
#define HELPERS_HEADER_GUARD
#include <cstdlib>
#include <set>
#include <utility>
#include "types.hpp"
std::set<BookID> ids;
std::set<BookID> freed_ids;
std::set<ShelfName> shelf_names;
#endif
并且shelf.cpp文件也出现在错误消息中:
#include <iostream>
#include <vector>
#include <exception>
#include <algorithm>
#include "bookshelf.hpp"
Bookshelf::Bookshelf(ShelfName shelf_name){
if(std::find(shelf_names.begin(), shelf_names.end(), shelf_name) != shelf_names.end()){
throw(std::invalid_argument("A bookshelf with the given name already exists."));
}
else{
shelf_name_ = shelf_name;
// content_ = {};
}
}
您正在将程序拆分为多个:
add_executable(main main.cpp)
add_executable(book src/book.cpp include/bookshelf.hpp include/book.hpp include/types.hpp include/helpers.hpp)
add_executable(bookshelf src/bookshelf.cpp include/bookshelf.hpp)
您只需要一个可执行文件。此外,头文件不属于那里:
add_executable(main main.cpp src/book.cpp src/bookshelf.cpp)
(顺便问一下,为什么main.cpp
不在src
中?(
另一方面,include_directories
应该只包括include
目录:
include_directories(
include
)
未定义引用错误的原因是,使用原始配置,CMake将创建三个独立的程序。只考虑这个:
add_executable(bookshelf src/bookshelf.cpp include/bookshelf.hpp)
它将通过编译src/bookshelf.cpp
来构建,但不使用src/book.cpp
。(.hpp
文件在这里应该不重要,但仍然不属于命令。(.
所以bookshelf.cpp
可能包含Book
类型的某个(成员(变量。为了使用这个变量,程序需要知道如何构造和销毁该类型的变量。换句话说,它需要有Book
的构造函数和析构函数的定义。但两者的定义仅在文件book.cpp
中,该文件不包括在此程序编译中。