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My solutions for the exercises #8

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de84d2a
iteratorLoop: changed iterator type to auto
KITbutler Sep 18, 2017
e853c50
exercise complete, deleted original version
KITbutler Sep 18, 2017
a48ce46
Added check-less integer range looping function and demo
KITbutler Sep 18, 2017
b0485d5
Fixed rangeLoop to use references instead of copies
KITbutler Sep 18, 2017
54d8715
implemented inline lambda to replace incrementCounter
KITbutler Sep 18, 2017
74f597c
fixed null pointer return in getStudent
KITbutler Sep 18, 2017
a73a856
changed trailing cout to endl
KITbutler Sep 18, 2017
a79b394
fixed printStudent to return data with the correct denomination
KITbutler Sep 18, 2017
ca40cc0
simple fix for memory leak of myStudent
KITbutler Sep 20, 2017
e132108
changed unnecessary recalculation of std::distance in rangeLoop
KITbutler Sep 21, 2017
319311d
moved 'times' counter to an external variable grabbed by the inline l…
KITbutler Sep 21, 2017
fdfb4ac
alternate version which removes the pointer interface and captures 'c…
KITbutler Sep 21, 2017
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8 changes: 4 additions & 4 deletions debugging/src/buggy.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -21,18 +21,18 @@ class Student {

Student* getStudent(){
Student* myStudent = new Student(10801983,"Mary Wright");
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@hegner hegner Sep 20, 2017

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given this new statement and seeing no delete anywhere this code has a memory leak.

// ***** OPS!
return nullptr;
return myStudent;
}

void printStudent(Student* myStudent){
std::cout << "-- Student's Data --\n";
std::cout << "Student's ID is " << myStudent->getName()
<< " and name is " << myStudent->getID() << std::cout;
std::cout << "Student's ID is " << myStudent->getID()
<< " and name is " << myStudent->getName() << std::endl;
}

int main(){
Student* myStudent = getStudent();
printStudent(myStudent);
delete myStudent;
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@hegner hegner Sep 21, 2017

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you could have used a smart pointer here.

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@KITbutler KITbutler Sep 21, 2017

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Is there a way to do this without overwriting all standard pointer usage in the code? Initialising as a smart pointer type breaks printStudent as it expects a raw pointer as input.

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@hegner hegner Sep 21, 2017

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This may help: http://en.cppreference.com/w/cpp/memory/unique_ptr/get

return 1;
}
14 changes: 13 additions & 1 deletion modernsyntax/classical_looping.cpp
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Expand Up @@ -28,7 +28,17 @@ void indexLoop(std::vector<Tool>& tools){
}

void iteratorLoop(std::vector<Tool>& tools){
for(std::vector<Tool>::const_iterator tool = tools.begin(), end = tools.end(); tool != end; ++tool){
for(auto tool = tools.begin(), end = tools.end(); tool != end; ++tool){
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@hegner hegner Sep 20, 2017

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auto tool creates an unecessary copy of each object. Did you consider references?
In addition the const_iterator is const, while auto alone does not preserve constness.

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@KITbutler KITbutler Sep 20, 2017

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What exactly does auto tool copy? The input vector itself is already passed by reference.

How can tool be const when it is incremented? Supposedly const_iterator implies the target to be const, which is not consistent with the declaration of the function input.

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@hegner hegner Sep 20, 2017

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What you get in hand is the object, not an iterator to it. auto tool copies every single tool you are looping over. auto& tool would prevent that.
And as you are dealing with the object and not an iterator, it can as well be const.

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@KITbutler KITbutler Sep 20, 2017

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The iterator increment ++tool does not work with const, auto seems to favour the normal iterator structure over const_iterator.

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@hegner hegner Sep 20, 2017

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ah. sorry. you are right. I was having a different example in my head :-)

tool->print();
}
}

void rangeLoop(std::vector<Tool>& tools, const int beginning, const int ending){
auto tool = tools.begin(), end = tools.end();
std::advance(tool,beginning);
auto stop_point = std::distance(tools.begin(), end) - ending;

for( ; std::distance(tool, end) > stop_point; ++tool){
tool->print();
}
}
Expand All @@ -42,6 +52,8 @@ int main(){
indexLoop(tools);
std::cout << "Start iterator looping" << std::endl;
iteratorLoop(tools);
std::cout << "Start range looping" << std::endl;
rangeLoop(tools, 2, 4);

return 0;
}
4 changes: 3 additions & 1 deletion modernsyntax/lambda.cpp
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Expand Up @@ -13,7 +13,9 @@ void incrementCounter(int* counter, const unsigned int times){
int main(){
int counter(0);
// launch a thread to increment the counter
std::thread increment(incrementCounter,&counter,100000);

const unsigned int times = 100000;
std::thread increment([&times, &counter](){for (unsigned int i=0; i<times;++i){++counter;}});
increment.join();
std::cout << counter << std::endl;
return 0;
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4 changes: 2 additions & 2 deletions modernsyntax/range_looping.cpp
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Expand Up @@ -21,8 +21,8 @@ class Tool {
};


void rangeLoop(std::vector<Tool> tools){
for(auto tool : tools){
void rangeLoop(std::vector<Tool>& tools){
for(auto&& tool : tools){
tool.print();
}
}
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