This chapter does not cover general debugging techniques—there are already plenty of good books about that topic. Instead, this chapter lists features that Qt provides specifically to help with debugging.
First, Qt provides the functions
are all declared in qglobal.h.
These functions work just like
printf() in that
they accept a format string and a variable number of parameters.
The advantage of these functions is that they work equally well
with Unix or Windows. In Unix, the output is written to standard
error. In Windows, it is sent to the debugger. In addition to
printing the message,
qFatal() exits the
program. All three functions restrict the text output to no more
than 8,196 characters, including the trailing zero byte.
If you want to redirect the output from these functions, you can install your own message handler. This is especially interesting because Qt contains hundreds of warning messages. Most warn the developer about invalid function parameters. Even though you should take all efforts to avoid provoking these warnings, you might want to rule out any possibility that your users will see them. A custom message handler can solve this problem.
Such a message handler is installed with the function
As its only argument, it expects the address of a function—the message
handler itself—with the following signature:
void (*)( QtMsgType type, const char *msg );
The second parameter is the message, ...