[C++知识库]OpenFOAM编程基础(2) - Input and output

本文是OpenFOAM编程基础系列文章的第2篇，也是自己学习的笔记，将随着学习的深入逐渐更新。本文的内容是在开源项目Basic OpenFOAM Programming Tutorials的基础上改写而来。由于原项目只有源代码和英文注释，本系列文章计划将代码进行分解、添加更加详细的注释，即是分享，也是自己学习。

从现在起，在运行案例前请检查案例的路径不包含空格！！否则会报错。

本文食用方法：

1. 你可以按顺序阅读，理解代码之后再下载案例代码自己运行；或者
2. 先跳到最后，下载案例代码，一遍读一边测试运行代码。

开始正文吧：

一个求解器的主程序（.c为后缀的文件）都会包含以下代码：

#include "fvCFD.H"

int main(int argc, char *argv[])
{
    // Initialise OF case
    #include "setRootCase.H"

    // These two create the time system (instance called runTime) and fvMesh (instance called mesh).
    #include "createTime.H"
    #include "createMesh.H"  

    // more code lines

    Info<< "End\n" << endl;
    return 0;
}

在编写新的求解器时，我们需要做的是根据需求在第12行的位置添加更多功能性代码。注意，程序的第9行需要检查./system/controlDict文件是否存在，并读取其中的设置参数，若不存在则会报错，求解器无法运行：

-->FOAM FATAL ERROR:
cannot find file "/mnt/BasicOpenFOAMProgrammingTutorials-master/helloWorld/system/controlDict"

同样，第10行代码则检查./constant文件下的网格文件是否存在， 若不存在同样会报错并退出运行：

--> FOAM FATAL ERROR:
Cannot find file "points" in directory "polyMesh" in times "0" down to constant

    From function virtual Foam::IOobject Foam::fileOperation::findInstance(const Foam::IOobject&, Foam::scalar, const Foam::word&) const
    in file global/fileOperations/fileOperation/fileOperation.C at line 871.

FOAM exiting

下面，将根据输入输出的数据类型分别讲解相应的代码。

1. OpenFOAM格式的字典文件

本案例以读取一个名为customProperties的字典为例。字典的内容如下：

FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "constant";
    object      transportProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

someWord myWord;

someScalar 0.01;

someBool on;

someList
(
    0
    1
    2
);

someHashTable
(
    key0 (0 0 0)
    key1 (1 0 0)
);

首先，现创建一个字典类型，指定文件名称、文件路径和读取要求：

    // Get access to a custom dictionary
    dictionary customDict;
    const word dictName("customProperties");

    // Create and input-output object - this holds the path to the dict and its name
    IOobject dictIO
    (
        dictName, // name of the file
        mesh.time().constant(), // path to where the file is: ./constant
        mesh, // reference to the mesh needed by the constructor
        IOobject::MUST_READ // indicate that reading this dictionary is compulsory
    );

可以采用以下代码检查输入的字典文件是否符合OpenFOAM的格式要求，检查通过后则将字典初始化：

    // Check the if the dictionary is present and follows the OF format
    if (!dictIO.typeHeaderOk<dictionary>(true))
        FatalErrorIn(args.executable()) << "Cannot open specified refinement dictionary "
            << dictName << exit(FatalError);
    // Initialise the dictionary object
    customDict = IOdictionary(dictIO);

下面，就可以从字典中读取信息了。这里我们使用.lookup函数实现。使用该函数不需要指定变量类型。

    // Lookup which does not need to be told what type of variable we're looking for and
    // uses the standard C++ stringstream syntax
    word someWord;
    customDict.lookup("someWord") >> someWord;

如果需要检查读取数据的类型，并且在读取的内容不存在时赋一个默认值，则可以使用以下代码：

    // This template method needs to know the type of the variable and can provide
    // a default value if the entry is not found in the dictionary
    scalar someScalar( customDict.lookupOrDefault<scalar>("someScalar", 1.0) );

也可以从字典中读取Bool类型的数据：

    // A switch is a neat feature allowing boolean values to be read from a dict,
    // it supports the OpenFOAM yes/on/true/1 and no/off/false/0 values automatically.
    bool someBool ( customDict.lookupOrDefault<Switch>("someBool",true) );

读取列表数据（List）和哈希表（HashTable）数据：

    // Lists of values may also be read in the same way
    List<scalar> someList ( customDict.lookup("someList") );

    // This type of container is particularly interesting - it associates entries with
    // given key values (here of word type but can be anything); useful when
    // associating things by indices in a list is less handy
    HashTable<vector,word> someHashTable ( customDict.lookup("someHashTable") );

最后，我们将所有读取到的数据输出到终端：

    // Summarise what's been read and print in the console
    Info << nl << "Read the following:" << nl << nl
         << "someWord " << someWord << nl << nl
         << "someScalar " << someScalar << nl << nl
         << "someList " << someList << nl << nl
         << "someHashTable " << someHashTable << nl << nl
         << "someBool " << someBool << nl << nl
         << endl;

2. 创建一个目录并写入一个输出文件

首先，在案例的根目录下创建一个名为postProcessing的文件夹，然后打开新创建的文件：

    // Create the output path directory; "Case/postProcessing"
    fileName outputDir = mesh.time().path()/"postProcessing"; 
    // Creathe the directory
    mkDir(outputDir);

    // File pointer to direct the output to
	autoPtr<OFstream> outputFilePtr;
    // Open the file in the newly created directory
    outputFilePtr.reset(new OFstream(outputDir/"customOutputFile.dat"));

向文件中写数据可以使用以下语句实现：

    // Write stuff
    outputFilePtr() << "# This is a header" << endl;
    outputFilePtr() << "0 1 2 3 4 5" << endl;

    // Append to the imported hash table and wirte it too
    someHashTable.insert("newKey", vector(1., 0., 0.));
    outputFilePtr() << someHashTable << endl;

3 案例文件下载

点击下载
提取码：cjkn