给出错误“未在此范围内声明”的结构向量
我有一个声明如下的结构：
#ifndef PLAYLIST_H
#define PLAYLIST_H
#include <iostream>
#include <string>
#include <vector>
#include "playlistitem.h"
#include "song.h"
#include "time.h"
struct Playlist {
std::vector<Song> songs;
Time cdTotalTime;
int totalTime;
};
和在另一个文件中声明的结构 Song：
#ifndef SONG_H
#define SONG_H
#include "playlist.h"
#include "time.h"
struct Song {
std::string title;
std::string artist;
std::string album;
int track;
Time length;
};
我在标头中都有两个结构定义，并且两者都应为 #included。
当我编译时出现错误
std:vector<Song> songs;
错误“歌曲”未在此范围内声明
我缺少什么？
I have a struct declared as follows:
#ifndef PLAYLIST_H
#define PLAYLIST_H
#include <iostream>
#include <string>
#include <vector>
#include "playlistitem.h"
#include "song.h"
#include "time.h"
struct Playlist {
std::vector<Song> songs;
Time cdTotalTime;
int totalTime;
};
and struct Song declared in another file:
#ifndef SONG_H
#define SONG_H
#include "playlist.h"
#include "time.h"
struct Song {
std::string title;
std::string artist;
std::string album;
int track;
Time length;
};
I have both struct definitions in headers, and both are #included as they should be.
When I compile I get an error at
std:vector<Song> songs;
error 'Song' was not declared in this scope
What am I missing?
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评论（5）
playlist.h 包含 Song.h
Song.h 不应包含 playlist.h
标头防护可防止无限递归，它们不会修复循环依赖关系。
目前song.h确实包含playlist.h。然后，当 playlist.h 包含 Song.h 时，没有任何反应（因为头保护），并且
Song未定义。因此 playlist.h 会产生错误。playlist.h includes song.h
song.h should NOT include playlist.h
Header guards prevent infinite recursion, they don't fix circular dependencies.
Currently song.h does include playlist.h. Then when playlist.h includes song.h, nothing happens (because of the header guard), and
Songis not defined. So playlist.h produces errors.不仅是您的主文件，声明
Playlist的文件也应该 #includeSong所在的文件。Not only your main file, but the file where
Playlistis declared should also #include the file whereSongis in.Song的定义必须位于Playlist定义中使用的定义之前。由于它们位于不同的标头中，因此您应该确保Playlist的标头包含Song的标头，并且两者都有适当的标头防护。The definition of
Songhas to come before its used in the definition ofPlaylist. Since they are in different headers, you should make sure that the header forPlaylistincludes that ofSong, and both have proper header guards.您的标头以循环方式相互包含。这是无用且不必要的。为什么您的
song.h包含playlist.h？从song.h中删除#include "playlist.h"即可修复该错误。Your headers include each other in circular fashion. This is useless and unnecessary. Why is your
song.hincludingplaylist.h? Remove#include "playlist.h"fromsong.hand that should fix the error.您可以通过放置
struct Song;在标头中原型Song，然后将标头包含在 .c/.cpp 文件中。这样做的好处是编译时间更快！ :D递归包含与包含防护一起工作得很好，只要你正确地安排它们。我总是尝试在 .h 文件中包含最少量的标头，将它们留给源文件。
另外，我在您的代码中没有看到#endif。现在我假设你的代码实际上有它；）
You could prototype
Songin your header by puttingstruct Song;and just include the header in your .c/.cpp file. This has the bonus of faster compile times! :DRecursive includes work fine with include guards, as long as you arrange them properly. I always try and include the least amount of headers in .h files, leaving them for the source files.
Also, I don't see a #endif on your code. Right now I'm assuming your code actually has it ;)