cmake未定义对函数的引用

Question

下面的项目结构是一个简化的例子。我试图将其归结为最少的文件来重现我的问题。

.
├── CMakeLists.txt
├── subdir1
│   ├── CMakeLists.txt
│   └── subsubdir1
│       ├── CMakeLists.txt
│       ├── Example.cpp
│       └── Example.h
└── subdir2
    ├── CMakeLists.txt
    ├── main.cpp
    └── subsubdir1
        ├── CMakeLists.txt
        ├── ExampleCreator.cpp
        └── ExampleCreator.h

./CMakeLists.txt

cmake_minimum_required(VERSION 2.8)
project(test)

macro(add_sources)
    file (RELATIVE_PATH _relPath "${CMAKE_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}")
    foreach (_src ${ARGN})
        if (_relPath)
            list (APPEND SRCS "${_relPath}/${_src}")
        else()
            list (APPEND SRCS "${_src}")
        endif()
    endforeach()
    if (_relPath)
        # propagate SRCS to parent directory
        set (SRCS ${SRCS} PARENT_SCOPE)
    endif()
endmacro()

add_subdirectory(subdir1)
add_subdirectory(subdir2)

add_executable(test ${SRCS})

subdir1/CMakeLists.txt

add_subdirectory(subsubdir1)

subdir1/subsubdir1/CMakeLists.txt

add_sources(Example.cpp)

subdir1/subsubdir1/Example.h

#ifndef EXAMPLE_H
#define EXAMPLE_H

class Example
{
public:
    Example();
    virtual ~Example();
};

#endif

subdir1/subsubdir1/Example.cpp

#include <stdio.h>
#include "Example.h"

Example::Example()
{
    printf("Inside Example constructor\n");
}

Example::~Example()
{
}

subdir2/CMakeLists.txt

add_subdirectory(subsubdir1)
add_sources(main.cpp)

subdir2/main.cpp

#include "subsubdir1/ExampleCreator.h"

int main(int argc, char** argv)
{
    ExampleCreator creator;
    return 0;
}

subdir2/subsubdir1/CMakeLists.txt

add_sources(ExampleCreator.cpp)

subdir2/subsubdir1/ExampleCreator.h

#ifndef EXAMPLE_CREATOR_H
#define EXAMPLE_CREATOR_H

class ExampleCreator
{
public:
    ExampleCreator();
    virtual ~ExampleCreator();
};

#endif

subdir2/subsubdir1/ExampleCreator.cpp

#include "ExampleCreator.h"
#include "../../subdir1/subsubdir1/Example.h"

ExampleCreator::ExampleCreator()
{
    Example* ex1 = new Example();
}

ExampleCreator::~ExampleCreator()
{
}

我希望这是对 CMake 如何处理依赖项的简单理解。这编译没有错误，但在链接期间失败。下面的make 输出显示Example.cpp 甚至没有编译，我不明白为什么。

user>:~/src/test/build$ make
Scanning dependencies of target test
[ 50%] Building CXX object CMakeFiles/test.dir/subdir2/subsubdir1/ExampleCreator.cpp.o
[100%] Building CXX object CMakeFiles/test.dir/subdir2/main.cpp.o
Linking CXX executable test
CMakeFiles/test.dir/subdir2/subsubdir1/ExampleCreator.cpp.o: In function `ExampleCreator::ExampleCreator()':
ExampleCreator.cpp:(.text+0x2b): undefined reference to `Example::Example()'
collect2: ld returned 1 exit status
make[2]: *** [test] Error 1
make[1]: *** [CMakeFiles/test.dir/all] Error 2
make: *** [all] Error 2

据我所知，所有来源都附加到根CMakeLists.txt 文件中的SRCS 变量中。那么，为什么不编译 Example.cpp 呢？或链接？

Answer 1

目录subdir1 不会生成二进制文件。添加这个：

project(Example)
add_library(Example Example.cpp)

而不是您的add_sources。在此之后，您需要告诉使用它链接它的项目：

TARGET_LINK_LIBRARIES(subdir2 Example)

如果您的名字不同，请记录下这些命令的功能。