C++ CMake没有这样的文件或目录

我在通过cmake构建Qt5项目时遇到问题

我运行命令

cmake..&&从目录
build
生成
，我收到以下错误：

/usr/bin/ld: cannot find -lengine-lib
collect2: error: ld returned 1 exit status
make[2]: *** [src/CMakeFiles/blacklist-engine-cli.dir/build.make:102: src/blacklist-engine-cli] Error 1
make[1]: *** [CMakeFiles/Makefile2:117: src/CMakeFiles/blacklist-engine-cli.dir/all] Error 2
make: *** [Makefile:84: all] Error 2

我已经简单地搜索了这个主题，但是当我在没有使用Qt5Sql的情况下运行这个项目时，仅使用Qt5Core，构建这个项目一点问题也没有。为了构建没有Qt5Sql的项目，我只需删除
db
文件夹，并删除其他CMakeLists.txt文件中引用的行。我的问题是:

如果我只想包含Qt5Core，为什么它可以工作？如果我还包含Qt5Sql，为什么它不工作？包括Qt5Sql在内，我做错了什么？

请不要包括与QtCreator或Qt安装错误相关的答案。我已经检查了我的Qt安装文件夹，并且在同一目录级别上安装了Qt5Core和Qt5Sql

我使用的是Ubuntu20.04，cmake版本3.16.3，Qt版本5.12.8

ls/usr/lib/x86_64-linux-gnu/cmake

Qt5 Qt5核心Qt5Gui Qt5 OpenGL Qt5打印支持Qt5测试Qt5Xml
QT5当前Qt5DBus QT5网络Qt5OpenGLExtensions Qt5Sql Qt5Widgets

我的项目中有以下结构：

root
├── CMakeModules
│   └── Qt.cmake
├── build
├── src
│   ├── db
│   │    ├── dbmanager.cpp
│   │    ├── dbmanager.h
│   │    └── CMakeLists.txt
│   ├── engine
│   │    ├── scanner.cpp
│   │    ├── scanner.h
│   │    └── CMakeLists.txt
│   ├── CMakeLists.txt
│   └── main.cpp
└── CMakeLists.txt

CMakeLists.txt：

cmake_minimum_required(VERSION 3.0)

project(blacklist-engine)

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

list(APPEND CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/CMakeModules)

add_subdirectory(src)

set(CMAKE_AUTOMOC ON)

find_package(Qt5 REQUIRED COMPONENTS Core Sql)

include(Qt)

add_subdirectory(
    db   
    engine
)

add_executable(blacklist-engine-cli main.cpp)

target_link_libraries(
    blacklist-engine-cli
    Qt5::Core
    Qt5::Sql
    engine-lib
    db-lib
)

#include <QtCore>

#include "db/dbmanager.h"
#include "engine/scanner.h"
...

set (db-lib-source
    dbmanager.h
    dbmanager.cpp
)

add_library(db-lib ${db-lib-source})

target_link_libraries(
    db-lib
    Qt5::Sql    
)

#include <QtSql/QSqlDatabase>
...

#include "dbmanager.h"

#include <QtSql/QSqlQuery>
...

set(engine-lib-source
    scanner.h
    scanner.cpp
)

add_library(engine-lib ${engine-lib-source})

#include <QtCore>
...

#include "scanner.h"
...

CMakeModules/Qt.cmake：

cmake_minimum_required(VERSION 3.0)

project(blacklist-engine)

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

list(APPEND CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/CMakeModules)

add_subdirectory(src)

set(CMAKE_AUTOMOC ON)

find_package(Qt5 REQUIRED COMPONENTS Core Sql)

include(Qt)

add_subdirectory(
    db   
    engine
)

add_executable(blacklist-engine-cli main.cpp)

target_link_libraries(
    blacklist-engine-cli
    Qt5::Core
    Qt5::Sql
    engine-lib
    db-lib
)

#include <QtCore>

#include "db/dbmanager.h"
#include "engine/scanner.h"
...

set (db-lib-source
    dbmanager.h
    dbmanager.cpp
)

add_library(db-lib ${db-lib-source})

target_link_libraries(
    db-lib
    Qt5::Sql    
)

#include <QtSql/QSqlDatabase>
...

#include "dbmanager.h"

#include <QtSql/QSqlQuery>
...

set(engine-lib-source
    scanner.h
    scanner.cpp
)

add_library(engine-lib ${engine-lib-source})

#include <QtCore>
...

#include "scanner.h"
...

src/CMakeLists.txt：

cmake_minimum_required(VERSION 3.0)

project(blacklist-engine)

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

list(APPEND CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/CMakeModules)

add_subdirectory(src)

set(CMAKE_AUTOMOC ON)

find_package(Qt5 REQUIRED COMPONENTS Core Sql)

include(Qt)

add_subdirectory(
    db   
    engine
)

add_executable(blacklist-engine-cli main.cpp)

target_link_libraries(
    blacklist-engine-cli
    Qt5::Core
    Qt5::Sql
    engine-lib
    db-lib
)

#include <QtCore>

#include "db/dbmanager.h"
#include "engine/scanner.h"
...

set (db-lib-source
    dbmanager.h
    dbmanager.cpp
)

add_library(db-lib ${db-lib-source})

target_link_libraries(
    db-lib
    Qt5::Sql    
)

#include <QtSql/QSqlDatabase>
...

#include "dbmanager.h"

#include <QtSql/QSqlQuery>
...

set(engine-lib-source
    scanner.h
    scanner.cpp
)

add_library(engine-lib ${engine-lib-source})

#include <QtCore>
...

#include "scanner.h"
...

src/main.cpp：

cmake_minimum_required(VERSION 3.0)

project(blacklist-engine)

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

list(APPEND CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/CMakeModules)

add_subdirectory(src)

set(CMAKE_AUTOMOC ON)

find_package(Qt5 REQUIRED COMPONENTS Core Sql)

include(Qt)

add_subdirectory(
    db   
    engine
)

add_executable(blacklist-engine-cli main.cpp)

target_link_libraries(
    blacklist-engine-cli
    Qt5::Core
    Qt5::Sql
    engine-lib
    db-lib
)

#include <QtCore>

#include "db/dbmanager.h"
#include "engine/scanner.h"
...

set (db-lib-source
    dbmanager.h
    dbmanager.cpp
)

add_library(db-lib ${db-lib-source})

target_link_libraries(
    db-lib
    Qt5::Sql    
)

#include <QtSql/QSqlDatabase>
...

#include "dbmanager.h"

#include <QtSql/QSqlQuery>
...

set(engine-lib-source
    scanner.h
    scanner.cpp
)

add_library(engine-lib ${engine-lib-source})

#include <QtCore>
...

#include "scanner.h"
...

src/db/dbmanager.h：

cmake_minimum_required(VERSION 3.0)

project(blacklist-engine)

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

list(APPEND CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/CMakeModules)

add_subdirectory(src)

set(CMAKE_AUTOMOC ON)

find_package(Qt5 REQUIRED COMPONENTS Core Sql)

include(Qt)

add_subdirectory(
    db   
    engine
)

add_executable(blacklist-engine-cli main.cpp)

target_link_libraries(
    blacklist-engine-cli
    Qt5::Core
    Qt5::Sql
    engine-lib
    db-lib
)

#include <QtCore>

#include "db/dbmanager.h"
#include "engine/scanner.h"
...

set (db-lib-source
    dbmanager.h
    dbmanager.cpp
)

add_library(db-lib ${db-lib-source})

target_link_libraries(
    db-lib
    Qt5::Sql    
)

#include <QtSql/QSqlDatabase>
...

#include "dbmanager.h"

#include <QtSql/QSqlQuery>
...

set(engine-lib-source
    scanner.h
    scanner.cpp
)

add_library(engine-lib ${engine-lib-source})

#include <QtCore>
...

#include "scanner.h"
...

src/engine/scanner.h：

cmake_minimum_required(VERSION 3.0)

project(blacklist-engine)

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

list(APPEND CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/CMakeModules)

add_subdirectory(src)

set(CMAKE_AUTOMOC ON)

find_package(Qt5 REQUIRED COMPONENTS Core Sql)

include(Qt)

add_subdirectory(
    db   
    engine
)

add_executable(blacklist-engine-cli main.cpp)

target_link_libraries(
    blacklist-engine-cli
    Qt5::Core
    Qt5::Sql
    engine-lib
    db-lib
)

#include <QtCore>

#include "db/dbmanager.h"
#include "engine/scanner.h"
...

set (db-lib-source
    dbmanager.h
    dbmanager.cpp
)

add_library(db-lib ${db-lib-source})

target_link_libraries(
    db-lib
    Qt5::Sql    
)

#include <QtSql/QSqlDatabase>
...

#include "dbmanager.h"

#include <QtSql/QSqlQuery>
...

set(engine-lib-source
    scanner.h
    scanner.cpp
)

add_library(engine-lib ${engine-lib-source})

#include <QtCore>
...

#include "scanner.h"
...

出现错误的原因是，从未构建
引擎库
，其CMake文件甚至从未处理过。CMake文件中有问题的行是：

add_subdirectory(
    db   
    engine
)

以这种方式使用时，第二个参数将成为与
db
相关的生成内容的二进制目录。因此，您可能会注意到CMake在
src/engine
目录中放置了一些构建工件，这可能不是您想要的

要解决此问题，必须连续调用
add_subdirectory
多次以包含多个子目录

add_subdirectory(db)
add_subdirectory(engine)

难道不是吗？谁否决了这个问题可以向我解释，我问这个问题错在哪里了？很抱歉，我是cmake的初学者，但我想我简单地提出了我的问题，我不明白你为什么要否决这个。。。我已经为这个问题挣扎了两天了。。。关于cmake还有很多其他的话题，只有两行，而且都是经过投票的。。。我不怪你对我投了反对票，只要解释一下我做错了什么以及我如何改进……我不明白你的
CMakeLists.txt
中的
include（Qt）
是为了什么。是否需要添加此包含目录？可能引擎库未成功生成。我不确定此问题被否决的原因。这是一个很好的、有充分记录的问题，表明这个问题已经被研究过了。