openfoam文件读取
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对于openfoam或其他c++程序而言，文件的读取是尤为重要的
我们最开始学习C++时，会学到类的初始化，或者是变量定义为某个值，再对某个值进行遍历，，，
类似如下：
点击查看代码
#include <iostream> // 包含头文件。
using namespace std; // 指定缺省的命名空间。
int main()
int a = 10;
int b = (10);
int c(10);
int e = 10;
int f 10 ;
cout << "a=" << a << endl;
cout << "b=" << b << endl;
cout << "c=" << c << endl;
cout << "e=" << e << endl;
cout << "f=" << f << endl;
尤其c++，初学时候内心非常感慨，怎么这么多初始化方式，我该用哪个
现在回头看，其实能熟悉一个，其他看懂就行，看不懂都没关系，毕竟我们还有gdb或者typeid()帮忙，可以看看这个变量类型具体是什么
说到底我们要问题导向目标导向，我们学习C++是为了类似openfoam这样的大工程服务的
那学这么多初始化赋值，有必要吗
如果是个大工程或者大程序是完全没必要的，
因为大工程的数据都是从文件或者数据库中获得的
你想想，要计算一个流体问题，如果有一万个网格，手打一万个三维位置就已经非常让人头疼了，更不要说上百个组分和压力等参数了，不现实
所以又回到了问题的起点，读取文件很重要，那么如何从文件中初始化程序，如何读取文件
在看of源码之前，不妨复习下C++是怎么读取文件的，进行下知识巩固
C++多使用fstream类或ifstream类
点击查看代码
#include <iostream>
#include <fstream> // ifstream类需要包含的头文件。
#include <string> // getline()函数需要包含的头文件。
using namespace std;
int main()
string filename = R"(./test.txt)";
//ifstream fin(filename, ios::in);
ifstream fin;
fin.open(filename , ios::in);
// 判断打开文件是否成功。
// 失败的原因主要有：1）目录不存在；2）文件不存在；3）没有权限，Linux平台下很常见。
if (fin.is_open() == false)
cout << "打开文件" << filename << "失败。\\n"; return 0;
string buffer;
while (fin >> buffer)
cout << buffer << endl;
fin.close(); // 关闭文件，fin对象失效前会自动调用close()。
cout << "操作文件完成。\\n";
OPENFOAM的文件读写，主要是用IOdictionary类
打开IOdictionary类的头文件，并不复杂
点击查看代码
class IOdictionary
:
public baseIOdictionary
public:
// Constructors
//- Construct given an IOobject
IOdictionary(const IOobject&);
//- Construct given an IOobject and dictionary
IOdictionary(const IOobject&, const dictionary&);
//- Construct given an IOobject and Istream
IOdictionary(const IOobject&, Istream&);
//- Copy constructor
IOdictionary(const IOdictionary&);
//- Move constructor
IOdictionary(IOdictionary&&);
//- Destructor
virtual ~IOdictionary();
// Member Functions
//- Is object global
virtual bool global() const
return true;
//- Return complete path + object name if the file exists
// either in the case/processor or case otherwise null
virtual fileName filePath() const
return globalFilePath(type());
// Member Operators
//- Move assignment
void operator=(IOdictionary&&);
;
继承于baseIOdictionary类，借助于IOobject接口有五个构造函数，这五个中一个移动构造一个拷贝构造，其他类继承可以创建自己成员函数global()和filePath()，头文件还对移动构造创建了等号赋值运算符
我们再看IOdictionary类的关键先生IOobject
IOobject就稍显复杂了，我们先看openfoam对其的描述：
IOobject defines the attributes of an object for which implicit objectRegistry management is supported, and provides the infrastructure for performing stream I/O.
An IOobject is constructed with an object name, a class name, an instance path, a reference to a objectRegistry, and parameters determining its storage status.
下面这张图是openfoam与该接口有关的类谱图
打开regIOobject类，这是个抽象类，openfoam对regIOobject的描述为：
regIOobject is an abstract class derived from IOobject to handle automatic object registration with the objectRegistry.
这里不赘述了，最后查了好半天，大概是哈希表来的，方便查询读取。openfoam中/0，/constant以及/system文件夹中那种奇怪的文件格式肯定有适合自己的读取方法。
那我们看看IOobject类相关源码，
IOobject类有四个枚举控制读取权限以及文件检查
点击查看代码
//- Enumeration defining the valid states of an IOobject
enum objectState
GOOD,
BAD
;
//- Enumeration defining the read options
enum readOption
MUST_READ,
MUST_READ_IF_MODIFIED,
READ_IF_PRESENT,
NO_READ
;
//- Enumeration defining the write options
enum writeOption
AUTO_WRITE = 0,
NO_WRITE = 1
;
//- Enumeration defining the file checking options
enum fileCheckTypes
timeStamp,
timeStampMaster,
inotify,
inotifyMaster
;
内共有六个构造函数，其中一个拷贝构造
点击查看代码
// Constructors
//- Construct from name, instance, registry, io options
IOobject
(
const word& name,
const fileName& instance,
const objectRegistry& registry,
readOption r=NO_READ,
writeOption w=NO_WRITE,
bool registerObject=true
);
//- Construct from name, instance, local, registry, io options
IOobject
(
const word& name,
const fileName& instance,
const fileName& local,
const objectRegistry& registry,
readOption r=NO_READ,
writeOption w=NO_WRITE,
bool registerObject=true
);
//- Construct from path, registry, io options
// Uses fileNameComponents() to split path into components.
IOobject
(
const fileName& path,
const objectRegistry& registry,
readOption r=NO_READ,
writeOption w=NO_WRITE,
bool registerObject=true
);
//- Construct from copy resetting registry
IOobject
(
const IOobject& io,
const objectRegistry& registry
);
//- Construct from copy resetting name
IOobject
(
const IOobject& io,
const word& name
);
//- Copy constructor
IOobject(const IOobject& io) = default;
我们举个例子，基于这些构造函数可以这样写类似这样的读取端口：
点击查看代码
IOobject dicName(
"dicName",
runTime.timeName(),
//runTime.constant(),
mesh,
IOobject::MUST_READ,
IOobject::AUTO_WRITE
) ;
再回到IOdictionary类，
通过查看IOdictionary类的构造函数，我们了解到可以在创建好的IOobject端口基础上构建，也可以直接构建IOobject端口
点击查看代码
IOdictionary dicName(
IOobject (
"dicName",
//runTime.constant(),
runTime.system(),
mesh,
IOobject::MUST_READ,
IOobject::AUTO_WRITE
)
) ;
那么我们如何通过IOdictionary类读取openfoam内文件呢，
以openfoam内置icoFoam为例
$ ls cavity/
0 constant system
$ tree cavity/
cavity/
├── 0
│ ├── U
│ └── p
├── constant
│ ├── polyMesh
│ │ ├── boundary
│ │ ├── faces
│ │ ├── neighbour
│ │ ├── owner
│ │ └── points
│ └── transportProperties
└── system
├── blockMeshDict
├── controlDict
├── fvSchemes
└── fvSolution
$ head cavity/0/* -n15
-
cavity/0/U *
/--------------------------------- C++ -----------------------------------
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 8
\\/ M anipulation |
*---------------------------------------------------------------------------*/
FoamFile
version 2.0;
format ascii;
class ** volVectorField;**
object U;
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // -
cavity/0/p *
/--------------------------------- C++ -----------------------------------
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: 8
\\/ M anipulation |
*---------------------------------------------------------------------------*/
FoamFile
version 2.0;
format ascii;
class ** volScalarField;**
object p;
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
从以上内容可以看到，U和v分别属于volVectorField类以及volScalarField类，那么就利用IOobject接口分别创建相关类如下所示：
点击查看代码
volVectorField U(
IOobject(
"U" ,
runTime.timeName() ,
mesh ,
IOobject::MUST_READ ,
IOobject::AUTO_WRITE
) ,
mesh
);
volScalarField p(
IOobject(
"p" ,
runTime.timeName() ,
mesh ,
IOobject::MUST_READ ,
IOobject::AUTO_WRITE
) ,
mesh
);
再看其他两个文件夹
$ grep -rn "dicti" .
./cavity/constant/transportProperties:12: class dictionary;
./cavity/system/controlDict:12: class dictionary;
./cavity/system/fvSolution:12: class dictionary;
./cavity/system/blockMeshDict:12: class dictionary;
./cavity/system/fvSchemes:12: class dictionary;
./constant/transportProperties:12: class dictionary;
./system/controlDict:12: class dictionary;
./system/fvSolution:12: class dictionary;
./system/blockMeshDict:12: class dictionary;
./system/fvSchemes:12: class dictionary;
都是dictionary类，那创建起来更方便了，比如说contorlDict文件
点击查看代码
IOdictionary controlDict(
IOobject (
"controlDict",
runTime.constant(),
//runTime.system(),
mesh,
IOobject::MUST_READ,
IOobject::AUTO_WRITE
)
) ;
有了dictionary这个字典类，顾名思义，字典当然是很方便查找啊，而且本身也是在链表以及哈希列表基础上建立的，能用的函数就很丰富了，如lookup()等。
综上，openfoam创建了一个读取方便查找容易的类支持of进行数据处理，寻根溯源很麻烦，但是用起来还是很简单的。
正因为文件读取占用很大的比重，这篇文章写了三个多小时，我们也是借此机会对openfoam内部略窥一二，这样我们就知道我们的程序在写什么，知道其所能为与不能为。
最后奉上自己编写的openfoam codesnip ，节约大家时间
点击查看代码
//***********************************************//
//openfoam
"Foam_IOobject":
"prefix": "IOobject_Foam_",
"body": [
"IOobject $1|U,p,T,dicName|(",
// "\\t$2|\\"U\\",\\"p\\",\\"T\\"|",
"\\t\\"$1\\",",
"\\t//runTime.timeName(),",
"\\t//runTime.constant(),",
"\\tmesh,",
"\\tIOobject::MUST_READ,",
"\\tIOobject::AUTO_WRITE",
") ;"
],
"description": "FOAM::IOobject"
,
"Foam::IOdictionary":
"prefix": "IOdictionary_Foam_",
"body": [
"IOdictionary $1:dicName(",
"\\tIOobject (",
// "\\t$2|\\"U\\",\\"p\\",\\"T\\"|",
"\\t\\t\\"$1\\",",
"\\t\\t//runTime.constant(),",
"\\t\\t//runTime.system(),",
"\\t\\tmesh,",
"\\t\\tIOobject::MUST_READ,",
"\\t\\tIOobject::AUTO_WRITE",
"\\t)",
") ;"
],
"description": "Foam::IOdictionary"
,
"Foam::volVectorField":
"prefix": "volVectorField_Foam_",
"body": [
"volVectorField $U(",
"\\tIOobject (",
"\\t\\t\\"$U\\",",
"\\t\\trunTime.timeName(),",
"\\t\\tmesh,",
"\\t\\tIOobject::MUST_READ,",
"\\t\\tIOobject::AUTO_WRITE",
"\\t),",
"\\tmesh",
") ;"
],
"description": "Foam::volVectorField"
,
"Foam::volScalarField":
"prefix": "volScalarField_Foam_",
"body": [
"volScalarField $p(",
"\\tIOobject (",
"\\t\\t\\"$p\\",",
"\\t\\trunTime.timeName(),",
"\\t\\tmesh,",
"\\t\\tIOobject::MUST_READ,",
"\\t\\tIOobject::AUTO_WRITE",
"\\t),",
"\\tmesh",
") ;"
],
"description": "Foam::volScalarField"
,
"Foam::scalar":
"prefix": "scalar",
"body": [
"scalar "
],
"description": "Foam::scalar"
,
//***********************************************//
创作不易，如若喜欢，不胜感激，欢迎支持，欢迎指正
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