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@ -57,8 +57,9 @@ Several functions that are described below take CvFileStorage\* as inputs and al |
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save or to load hierarchical collections that consist of scalar values, standard CXCore objects |
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(such as matrices, sequences, graphs), and user-defined objects. |
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OpenCV can read and write data in XML (<http://www.w3c.org/XML>) or YAML (<http://www.yaml.org>)
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formats. Below is an example of 3x3 floating-point identity matrix A, stored in XML and YAML files |
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OpenCV can read and write data in XML (<http://www.w3c.org/XML>), YAML (<http://www.yaml.org>) or
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JSON (<http://www.json.org/>) formats. Below is an example of 3x3 floating-point identity matrix A,
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stored in XML and YAML files |
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using CXCore functions: |
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XML: |
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@code{.xml} |
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@ -85,7 +86,8 @@ As it can be seen from the examples, XML uses nested tags to represent hierarchy |
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indentation for that purpose (similar to the Python programming language). |
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The same functions can read and write data in both formats; the particular format is determined by |
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the extension of the opened file, ".xml" for XML files and ".yml" or ".yaml" for YAML. |
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the extension of the opened file, ".xml" for XML files, ".yml" or ".yaml" for YAML and ".json" for |
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JSON. |
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*/ |
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typedef struct CvFileStorage CvFileStorage; |
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typedef struct CvFileNode CvFileNode; |
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@ -101,20 +103,20 @@ namespace cv { |
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/** @addtogroup core_xml
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XML/YAML file storages. {#xml_storage} |
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XML/YAML/JSON file storages. {#xml_storage} |
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======================= |
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Writing to a file storage. |
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-------------------------- |
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You can store and then restore various OpenCV data structures to/from XML (<http://www.w3c.org/XML>)
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or YAML (<http://www.yaml.org>) formats. Also, it is possible store and load arbitrarily complex
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data structures, which include OpenCV data structures, as well as primitive data types (integer and |
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floating-point numbers and text strings) as their elements. |
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You can store and then restore various OpenCV data structures to/from XML (<http://www.w3c.org/XML>),
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YAML (<http://www.yaml.org>) or JSON (<http://www.json.org/>) formats. Also, it is possible store
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and load arbitrarily complex data structures, which include OpenCV data structures, as well as |
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primitive data types (integer and floating-point numbers and text strings) as their elements. |
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Use the following procedure to write something to XML or YAML: |
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Use the following procedure to write something to XML, YAML or JSON: |
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-# Create new FileStorage and open it for writing. It can be done with a single call to |
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FileStorage::FileStorage constructor that takes a filename, or you can use the default constructor |
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and then call FileStorage::open. Format of the file (XML or YAML) is determined from the filename |
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extension (".xml" and ".yml"/".yaml", respectively) |
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and then call FileStorage::open. Format of the file (XML, YAML or JSON) is determined from the filename |
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extension (".xml", ".yml"/".yaml" and ".json", respectively) |
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-# Write all the data you want using the streaming operator `<<`, just like in the case of STL |
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streams. |
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-# Close the file using FileStorage::release. FileStorage destructor also closes the file. |
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@ -177,19 +179,19 @@ features: |
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- { x:344, y:158, lbp:[ 1, 1, 0, 0, 0, 0, 1, 0 ] } |
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@endcode |
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As an exercise, you can replace ".yml" with ".xml" in the sample above and see, how the |
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As an exercise, you can replace ".yml" with ".xml" or ".json" in the sample above and see, how the |
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corresponding XML file will look like. |
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Several things can be noted by looking at the sample code and the output: |
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- The produced YAML (and XML) consists of heterogeneous collections that can be nested. There are 2 |
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types of collections: named collections (mappings) and unnamed collections (sequences). In mappings |
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- The produced YAML (and XML/JSON) consists of heterogeneous collections that can be nested. There are |
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2 types of collections: named collections (mappings) and unnamed collections (sequences). In mappings |
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each element has a name and is accessed by name. This is similar to structures and std::map in |
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C/C++ and dictionaries in Python. In sequences elements do not have names, they are accessed by |
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indices. This is similar to arrays and std::vector in C/C++ and lists, tuples in Python. |
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"Heterogeneous" means that elements of each single collection can have different types. |
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Top-level collection in YAML/XML is a mapping. Each matrix is stored as a mapping, and the matrix |
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Top-level collection in YAML/XML/JSON is a mapping. Each matrix is stored as a mapping, and the matrix |
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elements are stored as a sequence. Then, there is a sequence of features, where each feature is |
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represented a mapping, and lbp value in a nested sequence. |
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@ -205,7 +207,7 @@ Several things can be noted by looking at the sample code and the output: |
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- To write a sequence, you first write the special string `[`, then write the elements, then |
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write the closing `]`. |
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- In YAML (but not XML), mappings and sequences can be written in a compact Python-like inline |
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- In YAML/JSON (but not XML), mappings and sequences can be written in a compact Python-like inline |
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form. In the sample above matrix elements, as well as each feature, including its lbp value, is |
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stored in such inline form. To store a mapping/sequence in a compact form, put `:` after the |
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opening character, e.g. use `{:` instead of `{` and `[:` instead of `[`. When the |
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@ -213,7 +215,7 @@ Several things can be noted by looking at the sample code and the output: |
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Reading data from a file storage. |
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--------------------------------- |
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To read the previously written XML or YAML file, do the following: |
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To read the previously written XML, YAML or JSON file, do the following: |
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-# Open the file storage using FileStorage::FileStorage constructor or FileStorage::open method. |
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In the current implementation the whole file is parsed and the whole representation of file |
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storage is built in memory as a hierarchy of file nodes (see FileNode) |
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@ -294,8 +296,8 @@ A complete example using the FileStorage interface |
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class CV_EXPORTS FileNode; |
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class CV_EXPORTS FileNodeIterator; |
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/** @brief XML/YAML file storage class that encapsulates all the information necessary for writing or reading
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data to/from a file. |
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/** @brief XML/YAML/JSON file storage class that encapsulates all the information necessary for writing or
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reading data to/from a file. |
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*/ |
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class CV_EXPORTS_W FileStorage |
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{ |
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@ -312,6 +314,7 @@ public: |
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FORMAT_AUTO = 0, //!< flag, auto format
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FORMAT_XML = (1<<3), //!< flag, XML format
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FORMAT_YAML = (2<<3), //!< flag, YAML format
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FORMAT_JSON = (3<<3), //!< flag, JSON format
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BASE64 = 64, //!< flag, write rawdata in Base64 by default. (consider using WRITE_BASE64)
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WRITE_BASE64 = BASE64 | WRITE, //!< flag, enable both WRITE and BASE64
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@ -333,9 +336,9 @@ public: |
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/** @overload
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@param source Name of the file to open or the text string to read the data from. Extension of the |
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file (.xml or .yml/.yaml) determines its format (XML or YAML respectively). Also you can append .gz |
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to work with compressed files, for example myHugeMatrix.xml.gz. If both FileStorage::WRITE and |
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FileStorage::MEMORY flags are specified, source is used just to specify the output file format (e.g. |
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file (.xml, .yml/.yaml, or .json) determines its format (XML, YAML or JSON respectively). Also you can |
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append .gz to work with compressed files, for example myHugeMatrix.xml.gz. If both FileStorage::WRITE |
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and FileStorage::MEMORY flags are specified, source is used just to specify the output file format (e.g. |
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mydata.xml, .yml etc.). |
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@param flags Mode of operation. See FileStorage::Mode |
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@param encoding Encoding of the file. Note that UTF-16 XML encoding is not supported currently and |
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@ -354,12 +357,12 @@ public: |
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See description of parameters in FileStorage::FileStorage. The method calls FileStorage::release |
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before opening the file. |
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@param filename Name of the file to open or the text string to read the data from. |
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Extension of the file (.xml or .yml/.yaml) determines its format (XML or YAML respectively). |
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Also you can append .gz to work with compressed files, for example myHugeMatrix.xml.gz. If both |
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Extension of the file (.xml, .yml/.yaml or .json) determines its format (XML, YAML or JSON |
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respectively). Also you can append .gz to work with compressed files, for example myHugeMatrix.xml.gz. If both |
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FileStorage::WRITE and FileStorage::MEMORY flags are specified, source is used just to specify |
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the output file format (e.g. mydata.xml, .yml etc.). A file name can also contain parameters. |
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You can use this format, "*?base64" (e.g. "file.xml?base64"), as an alternative to |
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FileStorage::BASE64 flag. Note: it is case sensitive. |
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You can use this format, "*?base64" (e.g. "file.json?base64" (case sensitive)), as an alternative to |
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FileStorage::BASE64 flag. |
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@param flags Mode of operation. One of FileStorage::Mode |
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@param encoding Encoding of the file. Note that UTF-16 XML encoding is not supported currently and |
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you should use 8-bit encoding instead of it. |
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MYLS
9 years ago