examples/SourceDestBufferStringCreate.cpp File Reference

example: creating SourceDestBuffers of Strings More...

Include dependency graph for SourceDestBufferStringCreate.cpp:

Functions
int	main (int, char **)
	Example use of ustring SourceDestBuffers.

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Detailed Description

example: creating SourceDestBuffers of Strings

Also see listing at end of this page for source without line numbers (to cut&paste from).

/*** SourceDestBufferStringCreate.cpp example: creating SourceDestBuffers of Strings */
#include <iostream>
#include "E57Foundation.h"
using namespace e57;
using namespace std;

int main(int /*argc*/, char** /*argv*/) {
    try {
        ImageFile imf("temp._e57", "w");
        StructureNode root = imf.root();
        
        StructureNode prototype(imf);
        prototype.set("s",  StringNode(imf));
        
        VectorNode codecs(imf, true);

        CompressedVectorNode cv(imf, prototype, codecs);
        root.set("cv1", cv);

        const int N = 2;
        vector<ustring> strings;
        strings.push_back("first string");
        strings.push_back("second string");
        vector<SourceDestBuffer> sbufs;
        sbufs.push_back(SourceDestBuffer(imf, "s", &strings));

        {
            CompressedVectorWriter writer = cv.writer(sbufs);
            writer.write(N);
            writer.close(); // don't forget to explicitly close the CompressedVectorWriter
        }

        imf.close(); // don't forget to explicitly close the ImageFile
    } catch(E57Exception& ex) {
        ex.report(__FILE__, __LINE__, __FUNCTION__);
        return(-1);
    }

    try {
        ImageFile imf("temp._e57", "r");
        StructureNode root = imf.root();

        CompressedVectorNode cv = static_cast<CompressedVectorNode> (root.get("cv1"));

        unsigned nChildren = static_cast<unsigned>(cv.childCount());
        vector<ustring> strings(nChildren);
        vector<SourceDestBuffer> dbufs;
        dbufs.push_back(SourceDestBuffer(imf, "s", &strings));

        {
            CompressedVectorReader reader = cv.reader(dbufs);
            unsigned nRead = reader.read();
            if (nRead != nChildren)
                return(-1);
            for (unsigned i = 0; i < nRead; i++)
                cout << "  string[" << i << "] = " << strings[i] << endl;
            reader.close(); // don't forget to explicitly close the CompressedVectorReader
        }

        imf.close(); // don't forget to explicitly close the ImageFile
    } catch(E57Exception& ex) {
        ex.report(__FILE__, __LINE__, __FUNCTION__);
        return(-1);
    }
    return(0);
}

This example program illustrates the writing and reading of StringNodes in a CompressedVectorNode. See the HelloWorld.cpp example for discussion of the use of include files, constructing an ImageFile, and the try/catch block to handle exceptions. See CompressedVectorCreate.cpp example for discussion about the writing/reading a CompressedVectorNode. See SourceDestBufferNumericCreate.cpp example for discussion about writing numbers in a CompressedVectorNode.

It is envisioned that for most uses of the E57 format, the fields of a CompressedVectorNode record will be entirely numeric. However it is possible to store Unicode strings in the record of a CompressedVectorNode (i.e. store strings in the compressed section of an E57 file). Writing and reading strings in a CompressedVectorNode are a little different than numbers: their values are not a known fixed width. Rather than using built-in C++ arrays as memory buffers to hold numbers, string use vector<ustring> buffers. The vector<ustring> has a fixed number of entries, just like the C++ arrays from numbers, but the length of each ustring in the vector can be different (i.e. sbuf[0].length() can be different than sbuf[1].length()).

Source lines 12-21 create a CompressedVectorNode that has a record that has a single string element s. Source lines 24-28 create a SourceDestBuffer that represents a two element vector that holds two ustrings of different lengths. Note that the third argument in the SourceDestBuffer constructor on source line 28, is the address of the vector to use, rather than the vector itself. Source lines 31-33 write the 2 strings to the CompressedVectorNode as a block.

In source lines 43-46, the E57 file is reopened for reading, and the CompressedVectorNode is fetched. An vector of strings is constructed in source line 49 which is large enough to hold all the strings from all the records defined (which is two records in this example), and a corresponding SourceDestBuffer is created in source line 50. The strings are read in one gulp on source line 55. The string values are printed on source lines 58-59. Repeated calls to CompressedVectorReader::read with a fixed length vector would be preferable in working code, as the number of records in a CompressedVectorNode is unbounded. Even with fetching a fixed number of strings on each read call, the amount of memory required is unknown because the strings read can be of any length.

Note that the string values written in the file do not appear in the XML listing, as they are stored in the binary section of the file that is not printed by the utility (E57xmldump.exe) that generated the listing. On XML line 4, you can see the fileOffset XML attribute that indicates the binary section that holds the CompressedVectorNode values starts at the physical offset of 40 (decimal) in the disk file.

The following console output is produced:

The XML section of the temp._e57 E57 file produced by this example program is as follows:

Here is the source code without line numbers to cut&paste from:

/*** SourceDestBufferStringCreate.cpp example: creating SourceDestBuffers of Strings */
#include <iostream>
#include "E57Foundation.h"
using namespace e57;
using namespace std;

int main(int /*argc*/, char** /*argv*/) {
    try {
        ImageFile imf("temp._e57", "w");
        StructureNode root = imf.root();
        
        StructureNode prototype(imf);
        prototype.set("s",  StringNode(imf));
        
        VectorNode codecs(imf, true);

        CompressedVectorNode cv(imf, prototype, codecs);
        root.set("cv1", cv);

        const int N = 2;
        vector<ustring> strings;
        strings.push_back("first string");
        strings.push_back("second string");
        vector<SourceDestBuffer> sbufs;
        sbufs.push_back(SourceDestBuffer(imf, "s", &strings));

        {
            CompressedVectorWriter writer = cv.writer(sbufs);
            writer.write(N);
            writer.close(); // don't forget to explicitly close the CompressedVectorWriter
        }

        imf.close(); // don't forget to explicitly close the ImageFile
    } catch(E57Exception& ex) {
        ex.report(__FILE__, __LINE__, __FUNCTION__);
        return(-1);
    }

    try {
        ImageFile imf("temp._e57", "r");
        StructureNode root = imf.root();

        CompressedVectorNode cv = static_cast<CompressedVectorNode> (root.get("cv1"));

        unsigned nChildren = static_cast<unsigned>(cv.childCount());
        vector<ustring> strings(nChildren);
        vector<SourceDestBuffer> dbufs;
        dbufs.push_back(SourceDestBuffer(imf, "s", &strings));

        {
            CompressedVectorReader reader = cv.reader(dbufs);
            unsigned nRead = reader.read();
            if (nRead != nChildren)
                return(-1);
            for (unsigned i = 0; i < nRead; i++)
                cout << "  string[" << i << "] = " << strings[i] << endl;
            reader.close(); // don't forget to explicitly close the CompressedVectorReader
        }

        imf.close(); // don't forget to explicitly close the ImageFile
    } catch(E57Exception& ex) {
        ex.report(__FILE__, __LINE__, __FUNCTION__);
        return(-1);
    }
    return(0);
}