在可执行文件中使用我自己的库时如何避免 "Undefined Reference" 错误，使用 CMake 构建项目？

Question

我正在尝试使用 CMake 建立一个 C++ 项目，但我想我遗漏了一些东西。当我尝试在可执行文件中使用我的库时出现错误：

Scanning dependencies of target dynamic-shadows-lib
[ 33%] Linking CXX static library libdynamic-shadows-lib.a
[ 33%] Built target dynamic-shadows-lib
Scanning dependencies of target main
[ 66%] Building CXX object CMakeFiles/main.dir/main.cpp.o
[100%] Linking CXX executable main
/usr/bin/ld: CMakeFiles/main.dir/main.cpp.o: in function `main':
main.cpp:(.text+0x83): undefined reference to `num3()'
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/main.dir/build.make:85: main] Error 1
make[1]: *** [CMakeFiles/Makefile2:78: CMakeFiles/main.dir/all] Error 2
make: *** [Makefile:84: all] Error 2

我的文件结构如下所示：

.
├── build
├── CMakeLists.txt
├── include
│   └── vec2f.hpp
├── main.cpp
└── src
    └── vec2f.cpp

3 directories, 4 files

我的根（也是唯一的）CMakeLists.txt 看起来像这样：

cmake_minimum_required(VERSION 3.16)

project(
    dynamic-shadows
    VERSION 1.0
    LANGUAGES CXX
)

# Set C++ to version 14
set(CMAKE_CXX_STANDARD 14)

# Set a name for the target
set(TARGET_LIB ${CMAKE_PROJECT_NAME}-lib)

# Make library ${TARGET_LIB}
add_library(${TARGET_LIB} STATIC)

# Set linker language to CXX (Gets error without it)
set_target_properties(${TARGET_LIB} PROPERTIES LINKER_LANGUAGE CXX)

# Set include directory for ${TARGET_LIB}
target_include_directories(
    ${TARGET_LIB}
    PUBLIC
        ${PROJECT_SOURCE_DIR}/include
)

# Set sources for ${TARGET_LIB} 
target_sources(
    ${TARGET_LIB} 
    PUBLIC
        ${PROJECT_SOURCE_DIR}/src
)

# Add a simple test executable to test the library
add_executable(main main.cpp)

# Link the ${TARGET_LIB} to main executable
target_link_libraries(
    main
    PUBLIC
        ${TARGET_LIB}
)

我怀疑问题出在我的 CMakeLists.txt 上，因为我是新手，但我不知道是什么问题。我错过了什么？难道是我做错了什么？

我尝试运行的代码非常简单，但我会把它包括在内以供参考：

./include/vec2.hpp

#ifndef __VEC2F_HPP__
#define __VEC2F_HPP__

#include <iostream>

namespace ds {

class vec2f {

public:
    float x;
    float y;

    vec2f(float x_value, float y_value) : x(x_value), y(y_value) {}
};

} // End of namespace ds

std::ostream & operator<<(std::ostream &out, const ds::vec2f &v);

ds::vec2f operator+(const ds::vec2f &left, const ds::vec2f &right);

float num3();

#endif

./src/vec2f.cpp

#include "../include/vec2f.hpp"

/**
 * @brief Overload of << operator for ds::vec2f class to allow for printing it in std::cout.
 * 
 * @param out std::ostream reference (&)
 * @param v ds::vec2f reference (&)
 * @return std::ostream& out
 */
std::ostream & operator<<(std::ostream &out, const ds::vec2f &v)
{
    return out << "[" << v.x << ", " << v.y << "]";
}

/**
 * @brief Overload of + operator for ds::vec2f class to allow for vector addition.
 * 
 * @param left ds::vec2f
 * @param right ds::vec2f
 * @return ds::vec2f sum
 */
ds::vec2f operator+(const ds::vec2f &left, const ds::vec2f &right)
{
    return ds::vec2f(
        left.x + right.x,
        left.y + right.y
    );
}

float num3()
{
    return 3;
}

./main.cpp

#include "vec2f.hpp"

int main(int argc, char* argv[])
{
    std::cout << "Hello world!" << std::endl;

    ds::vec2f v1 = ds::vec2f(8, -2);
    ds::vec2f v2 = ds::vec2f(2, 5);

    float n = num3();

    std::cout << "Res: " << n << std::endl;

    return 0;
}

我尝试遵循类似问题的解决方案，这些问题通常似乎与链接有关。

大多数都没有真正帮助，因为我需要使用 CMake 解决这个问题。我尝试了各种 CMakeLists.txt 配置，但最终还是选择了这个，因为它看起来最干净，而且似乎使用了最新的命令实现（target_include_directory 而不是 include_directories 等。 .)

Answer 1

# Set sources for ${TARGET_LIB} 
target_sources(
    ${TARGET_LIB} 
    PUBLIC
        ${PROJECT_SOURCE_DIR}/src
)

您添加源文件，而不是目录。只是：

 add_library(... STATIC
     src/vec2f.cpp
 )

不要使用PROJECT_SOURCE_DIR，当有人从上面使用add_subirectory时它会改变。如果你想要当前项目源目录，那就是 ${CMAKE_CURRENT_SOURCE_DIR}.

# Set linker language to CXX (Gets error without it)
set_target_properties(${TARGET_LIB} PROPERTIES LINKER_LANGUAGE CXX)

删除它。是的，没有源文件，没人知道你的库是什么语言的。

在可执行文件中使用我自己的库时如何避免 "Undefined Reference" 错误，使用 CMake 构建项目？

How to avoid "Undefined Reference" error when using my own library in an executable, building the project with CMake?

c++

cmake