C++ Requires Chilkat v11.7.0+

QR Code Error Correction Levels

See more QR Code Examples

Demonstrates the four QR error-correction levels. L, M, Q and H allow a reader to recover the data when about 7%, 15%, 25% and 30% of the symbol is damaged or covered. More error correction leaves less room for data, so the same text needs a larger symbol at a higher level. The default is M. The example also shows boostErrorCorrection, which raises the level for free when the chosen version has room to spare. C++

#include <CkFormats.h>
#include <CkJsonObject.h>
#include <CkJsonArray.h>

void ChilkatSample(void)
    {
    bool success = false;

    //  This example requires the Chilkat API to have been previously unlocked.
    //  See Global Unlock Sample for sample code.

    CkFormats fmt;
    CkJsonObject json;
    CkJsonObject jsonOut;
    json.UpdateString("payload.text","https://www.chilkatsoft.com/barcode_overview.asp");

    //  Encode the same text at each level.
    CkJsonArray levels;
    levels.Load("[\"L\",\"M\",\"Q\",\"H\"]");
    int i;
    for (i = 0; i <= 3; i++) {
        json.UpdateString("encoding.qr.errorCorrection",levels.stringAt(i));
        success = fmt.QrCode("generate",json,jsonOut);
        if (success == false) {
            std::cout << fmt.lastErrorText() << "\r\n";
            return;
        }

        std::cout << "level " << levels.stringAt(i) << ": version " << jsonOut.IntOf("symbols[0].selectedEncoding.version") << ", " << jsonOut.IntOf("symbols[0].dimensions.modulesWide")
             << " modules wide" << "\r\n";
    }

    //  The four symbols.  They hold the same text, and the higher the level, the larger the symbol:

    //  

    //  A symbol often has room left over.  boostErrorCorrection uses it: the level is raised
    //  as far as the same version allows, so the symbol is no larger but is more robust.
    CkJsonObject json2;
    json2.UpdateString("payload.text","https://chilkatsoft.com");
    json2.UpdateString("encoding.qr.errorCorrection","L");
    success = fmt.QrCode("generate",json2,jsonOut);
    if (success == false) {
        std::cout << fmt.lastErrorText() << "\r\n";
        return;
    }

    std::cout << "level L requested: version " << jsonOut.IntOf("symbols[0].selectedEncoding.version") << ", level " << jsonOut.stringOf("symbols[0].selectedEncoding.errorCorrection") << "\r\n";

    json2.UpdateBool("encoding.qr.boostErrorCorrection",true);
    success = fmt.QrCode("generate",json2,jsonOut);
    if (success == false) {
        std::cout << fmt.lastErrorText() << "\r\n";
        return;
    }

    std::cout << "level L with boost: version " << jsonOut.IntOf("symbols[0].selectedEncoding.version") << ", level " << jsonOut.stringOf("symbols[0].selectedEncoding.errorCorrection") << "\r\n";

    //  Level L, and level M reached by the boost.  The two symbols are the same size:

    //  

    //  Sample output:

    //  level L: version 3, 29 modules wide
    //  level M: version 4, 33 modules wide
    //  level Q: version 5, 37 modules wide
    //  level H: version 6, 41 modules wide
    //  level L requested: version 2, level L
    //  level L with boost: version 2, level M
    }