2017 c++SCB eFX IV#Dmitry

I feel these are all QQ type, as defined in https://bintanvictor.wordpress.com/2017/02/15/qqzz-mutual-exclusion-cjava/

Q: Scanning a vector of int (like finding the average or max). Forward iteration vs backward iteration, which one could be faster, considering all possible compiler optimizations.

%%A: forward. Memory read into cpu cache will be in chunks, not one element at a time. Easy for forward iteration. Not sure about backward.

Q: Which one could be fastest:

void f(double arg){…..}
void f(double & arg){….}

%%A: inlining for first but not 2nd?
A: See http://stackoverflow.com/questions/722257/should-i-take-arguments-to-inline-functions-by-reference-or-value esp. the long answer.

Q: Thr1 and Thr2 on 2 CPU’s both update an object s, having 2 fields. Thr1 only updats s.field1. Thr2 only updates s.field2. No interference. No synchronization required. We observe the performance is slower than using one thread to update both fields. Any explanation?

Q: weak_ptr justification, when we have shared_ptr already? I feel [[effectiveModernC++]] has a good chapter on it.

Ashish pointed out in some apps, you could identify a clear risk of circular dependency. Replace with weak_ptr.

Q: given an 2D array arr[10][5], how do you use pointer arithmetic to hit arr[1][5]

A: Contiguous. see http://stackoverflow.com/questions/7784758/c-c-multidimensional-array-internals. Note this is different from an array of pointers.

Q: what would you see if a TCP socket server has a full queue
%%A: TCP requires ack, so if server is unable to accept a request the client would know it.

Q: what STL algorithms did you use?
%%A: foreach(), find(), copy_if(), transform(), reverse()


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