Centos7 升级gcc版本并解决leveldb编译

前言

在Centos7上编译leveldb时报错

error: ‘is_trivially_copy_constructible’ is not a member of ‘std’

原因是Centos7默认装的gcc编译器版本低于5，一般需要额外加–std=c11参数才能用C++11的东西，不怎么会整Cmake，于是简单的解决办法就是升级gcc。注：本篇不考虑编译gcc源码的方案。

升级流程

1. 删除旧gcc

   yum remove gcc -y
   

2. 通过devtool安装gcc，这里以gcc7为例

    yum install centos-release-scl
    yum install devtoolset-7-gcc devtoolset-7-gcc-c++
   

3. 设置环境变量

   # devtool安装的gcc路径在/opt/rh/devtoolset-7/root/usr/bin下，所以需要处理下才能正常使用
   $ vi /etc/profile
   # 写入下面这句
   export PATH=$PATH:/opt/rh/devtoolset-7/root/usr/bin
   #保存完把终端重开一下
   

4. 验证

   [root@172 ~]# gcc --version
   gcc (GCC) 7.3.1 20180303 (Red Hat 7.3.1-5)
   Copyright (C) 2017 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.
   

leveldb编译问题处理

如果只是一般使用，上面那样配置后就没啥问题了，然而，编译leveldb时又报错：

[root@172 build]# cmake -DCMAKE_BUILD_TYPE=Release .. && cmake --build .
CMake Error at CMakeLists.txt:7 (project):
  The CMAKE_C_COMPILER:

    /usr/bin/cc

  is not a full path to an existing compiler tool.

  Tell CMake where to find the compiler by setting either the environment
  variable "CC" or the CMake cache entry CMAKE_C_COMPILER to the full path to
  the compiler, or to the compiler name if it is in the PATH.


CMake Error at CMakeLists.txt:7 (project):
  The CMAKE_CXX_COMPILER:

    /usr/bin/c++

  is not a full path to an existing compiler tool.

  Tell CMake where to find the compiler by setting either the environment
  variable "CXX" or the CMake cache entry CMAKE_CXX_COMPILER to the full path
  to the compiler, or to the compiler name if it is in the PATH.

不想改cmakelist，这里我只想到个土办法——软链接

[root@172 build]# ln -s /opt/rh/devtoolset-7/root/usr/bin/gcc /usr/bin/cc
[root@172 build]# ln -s /opt/rh/devtoolset-7/root/usr/bin/g++ /usr/bin/c++

重新执行编译命令

...
[ 94%] Building CXX object CMakeFiles/db_bench.dir/util/histogram.cc.o
[ 95%] Building CXX object CMakeFiles/db_bench.dir/util/testutil.cc.o
[ 96%] Building CXX object CMakeFiles/db_bench.dir/benchmarks/db_bench.cc.o
[ 97%] Linking CXX executable db_bench
[ 97%] Built target db_bench
[ 98%] Building CXX object third_party/googletest/googlemock/CMakeFiles/gmock_main.dir/src/gmock_main.cc.o
[ 98%] Linking CXX static library ../../../lib/libgmock_main.a
[ 98%] Built target gmock_main
[ 99%] Building CXX object third_party/benchmark/src/CMakeFiles/benchmark_main.dir/benchmark_main.cc.o
[100%] Linking CXX static library libbenchmark_main.a
[100%] Built target benchmark_main

成功了，不知道有没有其他更好的方法。