[C++知识库]error: ISO C++ forbids declaration of ‘point’ with no type [-fpermissive]

系统版本：Ubuntu16.04

问题描述：

刚开始跟着PCL tutorials官方教程学习PCL点云库，先创建pcd_write.cpp文件，然后编写CMakeLists.txt文件，官方提供的CMakeLists.txt文件内容如下：

cmake_minimum_required(VERSION 2.8 FATAL_ERROR)

project(pcd_write)

find_package(PCL 1.2 REQUIRED)

include_directories(${PCL_INCLUDE_DIRS})
link_directories(${PCL_LIBRARY_DIRS})
add_definitions(${PCL_DEFINITIONS})

add_executable (pcd_write pcd_write.cpp)
target_link_libraries (pcd_write ${PCL_LIBRARIES})

编译：

在当前目录下打开终端并进行cmake编译，

mkdir build
cd build
cmake ..
make

编译后报如下错误：

error: ISO C++ forbids declaration of ‘point’ with no type [-fpermissive]
   for (auto& point: cloud)
warning: range-based ‘for’ loops only available with -std=c++11 or -std=gnu++11
   for (auto& point: cloud)
error: request for member ‘y’ in ‘point’, which is of non-class type ‘int’
     point.y = 1024 * rand () / (RAND_MAX + 1.0f);
error: request for member ‘y’ in ‘point’, which is of non-class type ‘int’
     point.y = 1024 * rand () / (RAND_MAX + 1.0f);
error: request for member ‘z’ in ‘point’, which is of non-class type ‘int’
     point.z = 1024 * rand () / (RAND_MAX + 1.0f);

解决方案：

从第二句warning的警告可以知道基于范围的for循环仅适用于-std=c++11 或?-std=gnu++11标准，因此需要在CMakeLists.txt文件中加入C++11标准，最终的CMakeLists.txt文件内容如下：

cmake_minimum_required(VERSION 2.8 FATAL_ERROR)

# 指定为C++11 标准
set(CMAKE_CXX_STANDARD 11)

project(pcd_write)

find_package(PCL 1.2 REQUIRED)

include_directories(${PCL_INCLUDE_DIRS})
link_directories(${PCL_LIBRARY_DIRS})
add_definitions(${PCL_DEFINITIONS})

add_executable (pcd_write pcd_write.cpp)
target_link_libraries (pcd_write ${PCL_LIBRARIES})

接下来就可以顺利通过编译了。