C++11 and initialization

Uniform initialization in C++11 can be tricky.

Invocations mean something completely different and also give different results:

std::vector<int> v(1); // "normal" constructor invocation with (int) param - creates vector<int> with 1 element initialized to default value (i.e. 0)
std::vector<int> v{1}; // invocation of constructor with initializer_list<> param - content of initializer_list is copied into vector (i.e. one value of 1)


Following invocations also mean something completely different and give different results:

std::vector<int> v(1, 1); // "normal" constructor invocation with (int,int) params - creates vector<int> with 1 element initialized to specified value value (i.e. 1)
std::vector<int> v{1, 1}; // invocation of constructor with initializer_list<> param - content of initializer_list is copied into vector (i.e. two values of 1)


But following mean something completely different but give same results:

std::vector<int> v(2, 2); // "normal" constructor invocation with (int,int) params - creates vector<int> with 2 elements initialized to specified value value (i.e. 2)
std::vector<int> v{2, 2}; // invocation of constructor with initializer_list<> param - content of initializer_list is copied into vector (i.e. two values of 2)


Note that following will not compile:

std::vector<int> v(1, 1, 1); // no such "normal" constructor

whereas following is completely fine C++11 statement:

std::vector<int> v{1, 1, 1}; // invocation of constructor with initializer_list<> param - content of initializer_list is copied into vector (i.e. three values of 1)


Also note what is perhaps even more surprising that when container value type cannot be initialized from values in the list (no such conversion), then following construction will invoke "normal" constructor:

std::vector<std::string> v{1}; // same as - std::vector<std::string> v(1);


To avoid such behavior assign can be used in initialization (this is still construction, not assignment):

std::vector<std::string> v = {1}; // this will fail to compile
std::vector<int> v = {1}; // this will invoke initializer_list<> constructor as for std::vector<int> v{1};


There is even more about uniform initialization, especially using "auto" keyword - please check e.g. "Effective Modern C++" by Scott Meyers.
Also please check stackoverflow.

Thread-safe Catch

Catch test framework is nice, but not thread-safe - see https://github.com/philsquared/Catch/issues/99

There is thread-safe fork of Catch https://github.com/ned14/Catch-ThreadSafe
At the time of writing this original Catch is 1.2.1 whilst thread-safe fork 1.1

With or without you (exceptions)

To exception, or not to exception, that is the question.
What about cyclomatic complexity argument? E.g. http://programmers.stackexchange.com/questions/219872

upgradeable RW-locks - no, no

Never to be forgotten - upgradeable RW-locks always lead to deadlock.
I.e. when reader upgrades to writer without first leaving read lock, then other tread doing same lead to deadlock - no one moves back - deadlock.
Therefore:
- do not think on upgradeable RW-locks,
- if do so, then try-upgrade() function might be good approach, or
- deadlock detection, or
- 3rd user type - beside reader and writer - upgreadeableReader (like EnterUpgradeableReadLock from .NET). There can be only one upgreadeableReader (mutually exclusive). Normal readers cannot upgrade, therefore it is certain that only one user-reader will try to upgrade.

Redirect tcp to console (file) with awk

Sometimes useful, esp. when redirecting local tcp process output to console (file):

BEGIN {
NetService = "/inet/tcp/0/localhost/finger"
print "name" |& NetService
while ((NetService |& getline) > 0)
print $0
close(NetService)
}

More info @http://www.gnu.org/software/gawk/manual/gawkinet/gawkinet.html#Making-Connections

QNX specific commands

List of interesting (subjective) QNX-specific commands

• on - usually used for 2 reasons: start new process with specified priority and/or start new process on specific node (it makes possible to start process on different processor/system running QNX - working qnet is required - see Asymmetric multiprocessing (AMP))
• pidin - process list, frequently more useful than ps, top (e.g. options "-f A", "-f n","threads", "memory", "fds")
• coreinfo - allows for preliminary corefiles analysis directly on target without using gdb (note that in QNX coredumps are produced by dumper)
• use - info about specific command (e.g. "use devf-generic", "use -i devf-generic" - for build version)
• sendnto e.g. "sendnto -d /dev/ttyUSB1 qnx-ifs" (together with "cat /dev/ttyUSB1" and "echo 's' >/dev/ttyUSB1")

Best of StackOverflow

Subjective list of favorite StackOverfow questions

http://stackoverflow.com/questions/184618/what-is-the-best-comment-in-source-code-you-have-ever-encountered

http://stackoverflow.com/questions/381542/with-c-arrays-why-is-it-the-case-that-a5-5ahttp://stackoverflow.com/questions/11227809/why-is-processing-a-sorted-array-faster-than-an-unsorted-array
http://stackoverflow.com/questions/21947452/why-is-printing-b-dramatically-slower-than-printing
http://stackoverflow.com/questions/2501023/demonstrate-covariance-and-contravariance-in-java