c++ - grpc 找不到 protobuf 库

Question

我检查了 grpc 安装并完成了构建和安装。

现在当我尝试:

find_package(需要 gRPC 配置)

我明白了

CMake Error at CMakeLists.txt:15 (find_package):
  Found package configuration file:

    /usr/lib64/cmake/grpc/gRPCConfig.cmake

  but it set gRPC_FOUND to FALSE so package "gRPC" is considered to be NOT
  FOUND.  Reason given by package:

  The following imported targets are referenced, but are missing:
  protobuf::libprotobuf protobuf::libprotoc

虽然事件

find_package(需要 Protobuf)

工作得很好。

我读到我应该运行 cmake ../.. -DBUILD_DEPS=ON -DBUILD_SHARED_LIBS=ON 来解决这个问题。然而，这会导致:

CMake Error at cmake/abseil-cpp.cmake:38 (find_package):
  Could not find a package configuration file provided by "absl" with any of
  the following names:

    abslConfig.cmake
    absl-config.cmake

  Add the installation prefix of "absl" to CMAKE_PREFIX_PATH or set
  "absl_DIR" to a directory containing one of the above files.  If "absl"
  provides a separate development package or SDK, be sure it has been
  installed.
Call Stack (most recent call first):
  CMakeLists.txt:191 (include)


-- Configuring incomplete, errors occurred!
See also "/home/ray/CLionProjects/grpc/grpc/CMakeFiles/CMakeOutput.log".
See also "/home/ray/CLionProjects/grpc/grpc/CMakeFiles/CMakeError.log".

/usr/lib64/cmake/grpc/gRPCConfig.cmake 的内容

# Module path
list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_LIST_DIR}/modules)

# Depend packages






# Targets
include(${CMAKE_CURRENT_LIST_DIR}/gRPCTargets.cmake)

Answer 1

问题实际上出在您通过 find_package() 使用的项目及其包文件(/usr/lib64/cmake/grpc/gRPCConfig.cmake 在您的案子)。错误信息

The following imported targets are referenced, but are missing:

意味着，包文件引用了 IMPORTED 目标，但它们从未被定义。

该问题的常见原因如下:

1. 在其自己的构建过程中，该项目使用 find_package() 来获取其他一些包。此 find_package() 调用定义了 IMPORTED 目标，这些目标在项目中用于链接。

2. 它的包文件包含脚本，由install(EXPORT)命令创建，并根据install(TARGETS ... EXPORT ...) 命令。此包含的脚本使用 IMPORTED 目标，但未定义它们。

3. 项目的包文件忘记使用find_package，或者更好，find_dependency用于为包含的脚本定义 IMPORTED 目标。

如果你不想修复(其他)项目的包文件，那么最直接的解决办法是将遗漏的find_package添加到你自己的项目中:

# Hack: This will define IMPORTED targets, needed for gRPC project, but not defined by it.
find_package(Protobuf REQUIRED)
# Now perform the original 'find_package' call.
find_package(gRPC CONFIG REQUIRED)

---

实际上，gRPCConfig.cmake 包文件旨在包含调用 find_package(Protobuf)。它的模板cmake/gRPCConfig.cmake.in如下:

# Module path
list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_LIST_DIR}/modules)

# Depend packages
@_gRPC_FIND_ZLIB@
@_gRPC_FIND_PROTOBUF@
@_gRPC_FIND_SSL@
@_gRPC_FIND_CARES@
@_gRPC_FIND_ABSL@

# Targets
include(${CMAKE_CURRENT_LIST_DIR}/gRPCTargets.cmake)

并且在替换变量 _gRPC_FIND_PROTOBUF 时应该发出以下代码:

if(NOT Protobuf_FOUND AND NOT PROTOBUF_FOUND)
  find_package(Protobuf ${gRPC_PROTOBUF_PACKAGE_TYPE})
endif()

(变量应设置在 cmake/protobuf.cmake 中)。

但是出了点问题，结果 /usr/lib64/cmake/grpc/gRPCConfig.cmake 包含空变量的替换:

# Module path
list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_LIST_DIR}/modules)

# Depend packages






# Targets
include(${CMAKE_CURRENT_LIST_DIR}/gRPCTargets.cmake)