Undefined reference to QJson::Parser::Parser

Question

I've successfully(?) installed the QJson library following the instructions in the archive. But the compiler gives me this error:

Undefined reference to QJSon::Parser::Parser().

I've found where library files have been installed: it's /usr/local/include/json directory. But there are only *.h files in it.

The minimal code:

main.cpp

#include <QtGui/QApplication>
#include <qjson/parser.h>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QJson::Parser parser;
    return a.exec();
}

I use linux.

Where are *.cpp files? What did I do wrong? Why isn't the library complete?

score 2 · Accepted Answer · edited Jun 27 '12 at 13:52

2

At first you have to find a library file rather than a *.cpp file. Maybe it has a name like "libqjson.a" or "libqjson.so" and compile this library with your code or pass this keys to

g++ -L(lib path) -lqjson

As it turned out (see comments below), your library path is /usr/local/lib, so this line becomes:

g++ -L/usr/local/lib -lqjson

Using Qt (qmake), just add this line to your .pro file in order to pass these two flags to g++:

LIBS += -L/usr/local/lib -lqjson

edited Jun 27 '12 at 13:52

leemes

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answered Jun 27 '12 at 12:43

zapredelom

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Also note that the `lib path` isn't the include path (`/usr/local/include/json`). Maybe the library files are installed in `/usr/local/lib/...`? – leemes Jun 27 '12 at 12:50
yes maybe, also maybe in /usr/lib or in any folder if you defind prefix during instalation – zapredelom Jun 27 '12 at 12:56
@zapredelom i didn't define any prefixes – Ivan Akulov Jun 27 '12 at 13:32
@leemes there are libqjson.so, libqjson.so.0 and libqjson.0.7.1 files in /usr/local/lib dir. – Ivan Akulov Jun 27 '12 at 13:39
1

so just pass "-L /usr/local/lib" and "-lqjson" to gcc – zapredelom Jun 27 '12 at 13:46
Well... That's strange but I can't find compiler parameters in QtCreator. I've found build configuration, looked in Parameters->Build and Launch... – Ivan Akulov Jun 27 '12 at 13:48
1

... wihout the space after `-L`. Using Qt (qmake), just add this line to your `.pro` file in order to pass these two flags to g++: `LIBS += -L/usr/local/lib -lqjson` – leemes Jun 27 '12 at 13:50
@zapredelom g++, not gcc, since these are C++ files. – leemes Jun 27 '12 at 13:53

Undefined reference to QJson::Parser::Parser

1 Answers1