解决pip install dlib报错C++11 is required to use dlib

1.错误原因

在使用pip install dlib安装dlib的时候报错，

错误的详细信息如下：

ERROR: Command errored out with exit status 1:
command: /root/miniconda3/envs/cv_1/bin/python -u -c ‘import sys, setuptools, tokenize; sys.argv[0] = ‘"’"’/tmp/pip-install-jpjqw_8i/dlib_a6680215d7d4421581b7b4999664056c/setup.py’"’"’; file=’"’"’/tmp/pip-install-jpjqw_8i/dlib_a6680215d7d4421581b7b4999664056c/setup.py’"’"’;f=getattr(tokenize, ‘"’"‘open’"’"’, open)(file);code=f.read().replace(’"’"’\r\n’"’"’, ‘"’"’\n’"’"’);f.close();exec(compile(code, file, ‘"’"‘exec’"’"’))’ bdist_wheel -d /tmp/pip-wheel-pi50j_zu
cwd: /tmp/pip-install-jpjqw_8i/dlib_a6680215d7d4421581b7b4999664056c/
Complete output (76 lines):
running bdist_wheel
running build
running build_py
package init file ‘tools/python/dlib/init.py’ not found (or not a regular file)
running build_ext
Building extension for Python 3.6.13 |Anaconda, Inc.| (default, Jun 4 2021, 14:25:59)
Invoking CMake setup: ‘cmake /tmp/pip-install-jpjqw_8i/dlib_a6680215d7d4421581b7b4999664056c/tools/python -DCMAKE_LIBRARY_OUTPUT_DIRECTORY=/tmp/pip-install-jpjqw_8i/dlib_a6680215d7d4421581b7b4999664056c/build/lib.linux-x86_64-3.6 -DPYTHON_EXECUTABLE=/root/miniconda3/envs/cv_1/bin/python -DCMAKE_BUILD_TYPE=Release’
– The C compiler identification is GNU 11.2.0
– The CXX compiler identification is GNU 4.8.5
– Detecting C compiler ABI info
– Detecting C compiler ABI info - done
– Check for working C compiler: /usr/bin/cc - skipped
– Detecting C compile features
– Detecting C compile features - done
– Detecting CXX compiler ABI info
– Detecting CXX compiler ABI info - done
– Check for working CXX compiler: /usr/bin/c++ - skipped
– Detecting CXX compile features
– Detecting CXX compile features - done
– Found PythonInterp: /root/miniconda3/envs/cv_1/bin/python (found version “3.6.13”)
– Found PythonLibs: /root/miniconda3/envs/cv_1/lib/libpython3.6m.so
– Performing Test HAS_CPP14_FLAG
– Performing Test HAS_CPP14_FLAG - Failed
– Performing Test HAS_CPP11_FLAG
– Performing Test HAS_CPP11_FLAG - Success
– pybind11 v2.2.4
– Using CMake version: 3.21.2
– Compiling dlib version: 19.23.0
CMake Error at /tmp/pip-install-jpjqw_8i/dlib_a6680215d7d4421581b7b4999664056c/dlib/cmake_utils/set_compiler_specific_options.cmake:50 (message):
C++11 is required to use dlib, but the version of GCC you are using is too
old and doesn’t support C++11. You need GCC 4.9 or newer.
Call Stack (most recent call first):
/tmp/pip-install-jpjqw_8i/dlib_a6680215d7d4421581b7b4999664056c/dlib/cmake_utils/test_for_sse4/CMakeLists.txt:8 (include)

接下来我们找错误提示的重点信息：

C++11 is required to use dlib, but the version of GCC you are using is too
old and doesn’t support C++11. You need GCC 4.9 or newer.

2.原因分析

从错误信息上来看是由于gcc的版本低于4.9导致无法支持C++ 11，查看gcc的版本

				?

									#查看gcc的版本信息

									gcc --version

									:'

									gcc (GCC) 11.2.0

									Copyright (C) 2021 Free Software Foundation, Inc.

									This is free software; see the source for copying conditions.  There is NO

									warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

									'

从输出的gcc版本信息来看，不应该出错呀，因为gcc的版本已经大于4.9了。

出错的原因在于安装dlib的时候使用了conda的虚拟环境，而在环境内有一个低于4.9的gcc，而默认使用的正是这个版本，所以导致出错了。

3.解决办法

改变conda环境下的gcc版本：

1.查看conda环境下的gcc版本

				?

									gcc --version或gcc -v

2.替换gcc的版本

利用软连接来覆盖conda环境下的gcc版本

命令如下：

				?

									ln -s /usr/local/bin/gcc /home/name/anconda3/envs/env_name/bin/gcc

找不到conda中安装的gcc：

我就属于这种情况，在conda中找不到任何关于gcc的信息，在conda环境下使用gcc -v输出的版本也和没有使用conda环境输出的版本信息一致。

1.找到gcc的安装位置

				?

									which gcc

									#/usr/local/bin/gcc

2.导入环境变量

				?

									#激活conda环境

									source activate cv

									#设置环境变量

									export CC=/usr/local/bin/gcc

终极解决办法：

在环境外编译dlib的源码，生成whl文件，然后再环境内通过whl文件来安装dlib，

步骤如下：

				?

									#clone dlib的源码

									git clone https://github.com/davisking/dlib.git

									#编译dlib

									mkdir build; cd build; cmake .. ; cmake --build .

									#安装python版本的dlib

									python setup.py install