使用CMake链接libswscale失败：x86_64架构下sws_getContext符号未定义

核心排查方向及解决步骤： #

1. 修复C++与C库的符号兼容问题

FFmpeg全量库基于C语言实现，在C代码中直接引入其头文件时，编译器会对符号进行C风格的名字修饰，导致无法匹配库中的原生C符号。

修改video_writer.cpp中FFmpeg头文件的引入方式，用extern "C"包裹：

extern "C" {
#include <libswscale/swscale.h>
#include <libavcodec/avcodec.h>
#include <libavutil/pixfmt.h>
}

2. 调整链接顺序与依赖关系

链接器按从左到右的顺序解析符号，被依赖的库需要放在依赖它的库之后。尝试调整CMake中pkg-config的模块顺序，让libswscale优先被处理：

pkg_check_modules(LIBAV REQUIRED IMPORTED_TARGET
    libswscale
    libavcodec
    libavutil
)

3. 确认库架构与编译目标匹配

执行以下命令检查FFmpeg库的架构，确保与报错显示的x86_64一致：

lipo -info /usr/local/Cellar/ffmpeg/5.1.2/lib/libswscale.dylib

4. 验证pkg-config输出正确性

在终端运行以下命令，确认pkg-config返回的链接参数完整无遗漏：

pkg-config --libs --cflags libswscale libavcodec libavutil

将输出与CMake实际传递给链接器的参数对比，排查是否缺少必要的编译/链接选项。

原问题相关信息： #

报错信息：

Undefined symbols for architecture x86_64:
  "sws_getContext(int, int, AVPixelFormat, int, int, AVPixelFormat, int, SwsFilter*, SwsFilter*, double const*)", referenced from:
      VideoWriter::writeFrame(std::__1::vector<char, std::__1::allocator<char> >) in video_writer.cpp.o

调用代码：

struct SwsContext *sws_ctx = sws_getContext(
    avCodecContext->width, avCodecContext->height, AV_PIX_FMT_RGBA,
    avCodecContext->width, avCodecContext->height, AV_PIX_FMT_YUV420P,
    SWS_BILINEAR, NULL, NULL, NULL);

链接命令片段：

"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld" -demangle -lto_library /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/libLTO.dylib -no_deduplicate -dynamic -arch x86_64 -platform_version macos 10.15.0 11.1 -syslibroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk -o bin/main -search_paths_first -headerpad_max_install_names CMakeFiles/main.dir/src/main.cpp.o CMakeFiles/main.dir/src/window.cpp.o CMakeFiles/main.dir/src/video_writer.cpp.o -rpath /usr/local/lib /usr/local/lib/libGLEW.2.2.0.dylib /usr/local/lib/libboost_program_options-mt.dylib -framework OpenGL /usr/local/Cellar/sdl2_image/2.6.2/lib/libSDL2_image.dylib /usr/local/lib/libSDL2.dylib /usr/local/Cellar/ffmpeg/5.1.2/lib/libavcodec.dylib /usr/local/Cellar/ffmpeg/5.1.2/lib/libswscale.dylib /usr/local/Cellar/ffmpeg/5.1.2/lib/libavutil.dylib -lc++ -lSystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/12.0.0/lib/darwin/libclang_rt.osx.a -F/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/System/Library/Frameworks

CMake配置：

cmake_minimum_required(VERSION 3.19.2)

project(FragTool VERSION 1.0)

set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/cmake/")

# --- c++ build settings --- #
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED True)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Weffc++ -O0")
set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)

set(CMAKE_BUILD_TYPE Debug)

# --- dependencies --- #
find_package(GLEW REQUIRED)
find_package(Boost 1.79.0 COMPONENTS program_options REQUIRED)

find_package(PkgConfig REQUIRED)
pkg_check_modules(LIBAV REQUIRED IMPORTED_TARGET
    libavcodec
    libswscale
    libavutil
)

pkg_check_modules(LIBSDL2 REQUIRED IMPORTED_TARGET
    sdl2
    sdl2_image
)

set(EXECUTABLE main)
add_executable(${EXECUTABLE} src/main.cpp)
target_sources(${EXECUTABLE} PRIVATE
    ${CMAKE_SOURCE_DIR}/src/window.cpp
    ${CMAKE_SOURCE_DIR}/src/video_writer.cpp
)

target_include_directories(${EXECUTABLE} PRIVATE ${CMAKE_SOURCE_DIR}/src)
target_include_directories(${EXECUTABLE} PRIVATE ${GLEW_INCLUDE_DIRS})

target_link_libraries(${EXECUTABLE} PRIVATE GLEW::glew)
target_link_libraries(${EXECUTABLE} PRIVATE ${Boost_LIBRARIES})
target_link_libraries(${EXECUTABLE} PRIVATE PkgConfig::LIBSDL2)
target_link_libraries(${EXECUTABLE} PRIVATE PkgConfig::LIBAV)

内容的提问来源于stack exchange，提问作者J. Johnson