added API for storing OpenCV data structures to text string and reading them back

modules/core/doc/xml_yaml_persistence.rst

@@ -156,9 +156,9 @@ The constructors.
 
 .. ocv:function:: FileStorage::FileStorage()
 
-.. ocv:function:: FileStorage::FileStorage(const string& filename, int flags, const string& encoding=string())
+.. ocv:function:: FileStorage::FileStorage(const string& source, int flags, const string& encoding=string())
 
-    :param filename: Name of the file to open. Extension of the file (``.xml`` or ``.yml``/``.yaml``) determines its format (XML or YAML respectively). Also you can append ``.gz`` to work with compressed files, for example ``myHugeMatrix.xml.gz``.
+    :param source: Name of the file to open or the text string to read the data from. Extension of the file (``.xml`` or ``.yml``/``.yaml``) determines its format (XML or YAML respectively). Also you can append ``.gz`` to work with compressed files, for example ``myHugeMatrix.xml.gz``. If both ``FileStorage::WRITE`` and ``FileStorage::MEMORY`` flags are specified, ``source`` is used just to specify the output file format (e.g. ``mydata.xml``, ``.yml`` etc.).
 
     :param flags: Mode of operation. Possible values are:
 
@@ -167,6 +167,8 @@ The constructors.
         * **FileStorage::WRITE** Open the file for writing.
 
         * **FileStorage::APPEND** Open the file for appending.
+        
+        * **FileStorage::MEMORY** Read data from ``source`` or write data to the internal buffer (which is returned by ``FileStorage::release``)
 
     :param encoding: Encoding of the file. Note that UTF-16 XML encoding is not supported currently and you should use 8-bit encoding instead of it.
 
@@ -197,9 +199,9 @@ FileStorage::release
 --------------------
 Closes the file and releases all the memory buffers.
 
-.. ocv:function:: void FileStorage::release()
+.. ocv:function:: string FileStorage::release()
 
-Call this method after all I/O operations with the storage are finished.
+Call this method after all I/O operations with the storage are finished. If the storage was opened for writing data and ``FileStorage::WRITE`` was specified
 
 
 FileStorage::getFirstTopLevelNode

modules/core/include/opencv2/core/core.hpp

@@ -3941,7 +3941,12 @@ public:
     {
         READ=0, //! read mode
         WRITE=1, //! write mode
-        APPEND=2 //! append mode
+        APPEND=2, //! append mode
+        MEMORY=4,
+        FORMAT_MASK=(7<<3),
+        FORMAT_AUTO=0,
+        FORMAT_XML=(1<<3),
+        FORMAT_YAML=(2<<3)
     };
     enum
     {
@@ -3953,7 +3958,7 @@ public:
     //! the default constructor
     CV_WRAP FileStorage();
     //! the full constructor that opens file storage for reading or writing
-    CV_WRAP FileStorage(const string& filename, int flags, const string& encoding=string());
+    CV_WRAP FileStorage(const string& source, int flags, const string& encoding=string());
     //! the constructor that takes pointer to the C FileStorage structure
     FileStorage(CvFileStorage* fs);
     //! the destructor. calls release()
@@ -3964,7 +3969,7 @@ public:
     //! returns true if the object is associated with currently opened file.
     CV_WRAP virtual bool isOpened() const;
     //! closes the file and releases all the memory buffers
-    CV_WRAP virtual void release();
+    CV_WRAP virtual string release();
 
     //! returns the first element of the top-level mapping
     CV_WRAP FileNode getFirstTopLevelNode() const;

modules/core/include/opencv2/core/types_c.h

@@ -1740,6 +1740,11 @@ typedef struct CvFileStorage CvFileStorage;
 #define CV_STORAGE_WRITE_TEXT    CV_STORAGE_WRITE
 #define CV_STORAGE_WRITE_BINARY  CV_STORAGE_WRITE
 #define CV_STORAGE_APPEND        2
+#define CV_STORAGE_MEMORY        4
+#define CV_STORAGE_FORMAT_MASK   (7<<3)
+#define CV_STORAGE_FORMAT_AUTO   0
+#define CV_STORAGE_FORMAT_XML    8
+#define CV_STORAGE_FORMAT_YAML  16
 
 /* List of attributes: */
 typedef struct CvAttrList

modules/core/test/test_io.cpp

@@ -91,7 +91,7 @@ protected:
             {-1000000, 1000000}, {-10, 10}, {-10, 10}};
         RNG& rng = ts->get_rng();
         RNG rng0;
-        test_case_count = 2;
+        test_case_count = 4;
         int progress = 0;
         MemStorage storage(cvCreateMemStorage(0));
         
@@ -102,9 +102,10 @@ protected:
             
             cvClearMemStorage(storage);
             
+            bool mem = (idx % 4) >= 2;
             string filename = tempfile(idx % 2 ? ".yml" : ".xml");
             
-            FileStorage fs(filename.c_str(), FileStorage::WRITE);
+            FileStorage fs(filename, FileStorage::WRITE + (mem ? FileStorage::MEMORY : 0));
             
             int test_int = (int)cvtest::randInt(rng);
             double test_real = (cvtest::randInt(rng)%2?1:-1)*exp(cvtest::randReal(rng)*18-9);
@@ -179,11 +180,11 @@ protected:
             fs.writeObj("test_graph",graph);
             CvGraph* graph2 = (CvGraph*)cvClone(graph);
             
-            fs.release();
+            string content = fs.release();
             
-            if(!fs.open(filename.c_str(), FileStorage::READ))
+            if(!fs.open(mem ? content : filename, FileStorage::READ + (mem ? FileStorage::MEMORY : 0)))
             {
-                ts->printf( cvtest::TS::LOG, "filename %s can not be read\n", filename.c_str() );
+                ts->printf( cvtest::TS::LOG, "filename %s can not be read\n", !mem ? filename.c_str() : content.c_str());
                 ts->set_failed_test_info( cvtest::TS::FAIL_MISSING_TEST_DATA );
                 return;
             }
@@ -310,7 +311,6 @@ protected:
             int real_width = (int)tm["width"];
             int real_height = (int)tm["height"];
             
-            
             int real_lbp_val = 0;
             FileNodeIterator it;
             it = tm_lbp.begin();
@@ -370,7 +370,8 @@ protected:
             }
             
             fs.release();
-            remove(filename.c_str());
+            if( !mem )
+                remove(filename.c_str());
         }
     }
 };