如何用CMake构建含同级client与common目录的可执行文件？编译报错求助

Let's break down what's causing your build error and fix the CMakeLists.txt step by step.

Root Cause of the Error #

The main issues in your current script are:

1. You tried to link a directory path (${common_dir}) in target_link_libraries, which CMake interprets as a target it needs to build—hence the "No rule to make target '../common'" error.
2. The add_library(common_src) line is incomplete: you didn't provide the source files for the common library.
3. You're mixing two approaches for common sources (adding them directly to the executable and creating a library for them) which creates confusion.

Corrected CMakeLists.txt #

Here's the fixed version that builds your executable properly, using a clean library-based approach for common code:

cmake_minimum_required(VERSION 3.1.0)
project(Client)

set(common_dir ${PROJECT_SOURCE_DIR}/common)
include_directories(${common_dir})

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON) # Enforce the C++17 standard
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)
set(CMAKE_AUTOUIC ON)

# Remove redundant -std=c++17 flag (CMAKE_CXX_STANDARD already handles this)
# set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++17")

if (CMAKE_BUILD_TYPE STREQUAL "RELEASE")
    add_definitions(-DQT_NO_DEBUG_OUTPUT)
endif()

if(CMAKE_VERSION VERSION_LESS "3.7.0")
    set(CMAKE_INCLUDE_CURRENT_DIR ON)
endif()

IF(WIN32)
    SET(OS_SPECIFIC_LIBS netapi32 wsock32)
ENDIF()

# Group Qt component lookup for readability
find_package(Qt5 COMPONENTS 
    Core Widgets Gui Network Svg PrintSupport WebSockets
REQUIRED)

# Gather source files
file(GLOB client_src "*.h" "*.cpp" "Resources.qrc")
file(GLOB common_src "${common_dir}/*.h" "${common_dir}/*.cpp")

# Create a static library for common code (fixes the incomplete add_library call)
add_library(common_lib STATIC ${common_src})

# Link common library against Qt dependencies it may use
target_link_libraries(common_lib Qt5::Core Qt5::Network)

# Build the client executable, link against common library and Qt components
add_executable(Client ${client_src})
target_link_libraries(Client 
    common_lib 
    Qt5::Core Qt5::Widgets Qt5::Gui Qt5::Network 
    Qt5::Svg Qt5::PrintSupport Qt5::WebSockets 
    ${OS_SPECIFIC_LIBS}
)

Key Modifications Explained #

• Fixed common library setup: Changed add_library(common_src) to add_library(common_lib STATIC ${common_src})—this properly creates a static library from your common directory sources with a clear, usable target name.
• Removed invalid directory link: Took ${common_dir} out of target_link_libraries—we now link against the common_lib target instead of a directory path.
• Linked common library to Qt: Added target_link_libraries(common_lib Qt5::Core Qt5::Network) to ensure any Qt-dependent code in your common sources has access to required libraries.
• Cleaned up C++ standard: Removed the redundant -std=c++17 flag (handled by CMAKE_CXX_STANDARD) and added CMAKE_CXX_STANDARD_REQUIRED ON to enforce compliance.
• Simplified Qt lookup: Grouped all Qt components into a single find_package call for better readability.

Alternative: Compile All Sources Directly #

If you don't want a separate library for common code, you can simplify the script to compile all sources directly into the executable:

# ... keep all setup code above ...

# Gather all sources in one go
file(GLOB all_sources 
    "*.h" "*.cpp" "Resources.qrc"
    "${common_dir}/*.h" "${common_dir}/*.cpp"
)

add_executable(Client ${all_sources})
target_link_libraries(Client 
    Qt5::Core Qt5::Widgets Qt5::Gui Qt5::Network 
    Qt5::Svg Qt5::PrintSupport Qt5::WebSockets 
    ${OS_SPECIFIC_LIBS}
)

Note: Using file(GLOB) can miss new files added later—for more robust builds, consider listing sources explicitly instead of relying on glob patterns.

内容的提问来源于stack exchange，提问作者Antonio Santoro