Everyone agrees that internal state checking using assert(), Q_ASSERT(), assert are good. Programmer can declare expected input (asserting parameters), internal state (invariants) and verify return values (postconditions) and runtime will verify such expectations. There are languages with direct support for assertions in those three variants (Eiffel with his Design By Contract philosophy).
Those assertions typically will show filename/line number/message information and abort program / raise an exception if the condition is not met. Runtime environment then can collect current stacktrace to give developer more information on failed expectation.
One can disable assertions entirely (C++, Java) or select subset of assertions (Eiffel) for production releases. Resulting code will be faster, but failed expectations will not be verified by software – problem reports may be harder to interpret.
On the other hand if an assertion is too strict (the assumption may be invalid) it may abort program giving user negative impression about software stability.
What to do then? How can we keep problem-diagnosing power of enabled assertions and prevent minor of invalid failed assertions from aborting whole program?
The answer is: weak assertions (assertion without abort).
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My current project I’m working on is based on embedded systems and QT platform. Of course the very first task in the project is to implement some kind of testing method to get feedback on software quality. The test system is composed from few components:
- Automatic crash reports collected on central server
- Automatic random test runners connected to always-running (24/7) devices to catch crashes
First channel collects all crashes (from human and automated tests), second channel is performed fully automatically. Second channel allows to measure MMTF (mean time between failures) and analyse changes in time, probably helping with estimating current software quality state.
Second testing channel requires automatic test driver to inject random UI events (key presses, remote in my case). I used QT message queue for that purpose:
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Collecting runtime errors (crashes, failed assertions, …) is very important part of software quality efforts. If you know crash details from your testing team you can handle them even before a tester writes first line of error report (!). That improves development speed.
Probably the fastest method how to create KISS (Keep It Simple Stupid) central crash report repository is to use:
- netcat – command line UDP server
- crontab – for daily logs rotation
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Dereferencing NULL pointer is a very common programming error in almost any programming language that supports pointers. It cannot be caught at build time in general, so we can carefully check every pointer before dereference and handle errant cases in runtime (warning in log?).
But above method is a runtime method. If you don’t have proper code coverage by tests it might not detect errant cases. I believe the answer for this issue lies in static methods (performed at build/before runtime phase). Good example of such approach is LCLint:
char firstChar2 (/*@null@*/ char *s)
{
if (isNull (s)) return '\0';
return *s;
}
As you can see LCLint uses annotations to mark parameter that might have NULL value and thus can detect dereferencing NULL. But LCList is only designed for C language and cannot check C++ (C++ is more complicated for parsing).
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C++ compiler is pretty big and slow tool and if one needs to make full rebuilds very often waiting for build finish is very frustrating. For those guys “ccache” tool was created.
How is it working? Compiler output (*.o files) are cached under key that is computed from preprocessed source code, compiler versions, build switches. This way builds might be much faster.
Qmake is a Makefile generator that comes with QT and allows for easy build of QT-based (and other) projects. In order to join ccache and qmake one have to update so called “mkspecs” files. How to do that?
It’s easy using sed (I’m including only sh4 and mipsel crosscompiler toolchains):
# sed -i '/QMAKE_CXX .*= *[^c][^c]/s/= /= ccache /' \
`find /usr/local -name qmake.conf | grep 'linux-\(sh4\|mipsel\)'`
And how to revert:
# sed -i '/ccache/s/ccache / /' \
`find /usr/local -name qmake.conf | grep 'linux-\(sh4\|mipsel\)'`
Of course you can manually launch an editor and update those files, but a bit of sed scripting is many times faster 
