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qrencode Documentation


qrencode - QR Code encoder

Copyright (C) 2006, 2007, 2008, 2009 Kentaro Fukuchi <fukuchi@megaui.net>

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA Libqrencode is a library for encoding data in a QR Code symbol, a kind of 2D symbology.


There are two ways to encode data: encoding a string or encoding a structured data.

Encoding a string

You can encode a string by calling QRcode_encodeString(). The given string is parsed automatically and encoded. If you want to encode data that can be represented as a C string style (NUL terminated), you can simply use this way.

If the input data contains Kanji (Shift-JIS) characters and you want to encode them as Kanji in QR Code, you should give QR_MODE_KANJI as a hint. Otherwise, all of non-alphanumeric characters are encoded as 8 bit data. If you want to encode a whole string in 8 bit mode, use QRcode_encodeString8bit() instead.

Please note that a C string can not contain NUL character. If your data contains NUL, you should chose the second way.

Encoding a structured data

You can construct a structured input data manually. If the structure of the input data is known, you can use this way. At first, create a QRinput object by QRinput_new(). Then add input data to the QRinput object by QRinput_append(). Finally call QRcode_encodeInput() to encode the QRinput data. You can reuse the QRinput data again to encode it in other symbols with different parameters.


The encoded symbol is resulted as a QRcode object. It will contain its version number, width of the symbol and an array represents the symbol. See QRcode for the details. You can free the object by QRcode_free().

Please note that the version of the result may be larger than specified. In such cases, the input data would be too large to be encoded in a symbol of the specified version.

Structured append

Libqrencode can generate "Structured-appended" symbols that enables to split a large data set into mulitple QR codes. A QR code reader concatenates multiple QR code symbols into a string. Just like QRcode_encodeString(), you can use QRcode_encodeStringStructured() to generate structured-appended symbols. This functions returns an instance of QRcode_List. The returned list is a singly-linked list of QRcode: you can retrieve each QR code in this way:

 QRcode_List *qrcodes;
 QRcode_List *entry;
 QRcode *qrcode;

 qrcodes = QRcode_encodeStringStructured(...);
 entry = qrcodes;
 while(entry != NULL) {
     qrcode = entry->code;
     // do something
     entry = entry->next;

Instead of using auto-parsing functions, you can construct your own structured input. At first, instantiate an object of QRinput_Struct by calling QRinput_Struct_new(). This object can hold multiple QRinput, and one QR code is generated for a QRinput. QRinput_Struct_appendInput() appends a QRinput to a QRinput_Struct object. In order to generate structured-appended symbols, it is required to embed headers to each symbol. You can use QRinput_Struct_insertStructuredAppendHeaders() to insert appropriate headers to each symbol. You should call this function just once before encoding symbols.

QR Code encoder into PNG image
Qrencode is a utility software using libqrencode to encode string data in
a QR Code and save as a PNG image.
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