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July 17, 2015 20:14
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Differences in Vector Allocation / Deallocation between C++ Versions
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[cswiercz@clavius vectors] clang++ ./construction.cpp && ./a.out | |
========================= | |
===== Experiment #1 ===== | |
========================= | |
Resizing and new element construction | |
-- v.resize(3) | |
-- resizing members | |
[#0] constructed | |
[#1] constructed | |
[#2] constructed | |
-- v.capacity() = 3 | |
-- v.resize(4) | |
[#3] copy constructed (from element [#2]) | |
[#4] copy constructed (from element [#1]) | |
[#5] copy constructed (from element [#0]) | |
[#2] destroyed | |
[#1] destroyed | |
[#0] destroyed | |
===== END ===== | |
[#3] destroyed | |
[#4] destroyed | |
[#5] destroyed | |
========================= | |
===== Experiment #2 ===== | |
========================= | |
Using push_back. | |
-- v.resize(3) | |
-- pushing elements back | |
[#0] constructed | |
[#1] copy constructed (from element [#0]) | |
[#0] destroyed | |
[#2] constructed | |
[#3] copy constructed (from element [#2]) | |
[#2] destroyed | |
[#4] constructed | |
[#5] copy constructed (from element [#4]) | |
[#4] destroyed | |
-- v.capacity() = 3 | |
-- v.resize(4) | |
[#6] copy constructed (from element [#5]) | |
[#7] copy constructed (from element [#3]) | |
[#8] copy constructed (from element [#1]) | |
[#5] destroyed | |
[#3] destroyed | |
[#1] destroyed | |
===== END ===== | |
[#6] destroyed | |
[#7] destroyed | |
[#8] destroyed |
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[cswiercz@clavius vectors] clang++ --std=c++11 ./construction.cpp && ./a.out | |
========================= | |
===== Experiment #1 ===== | |
========================= | |
Resizing and new element construction | |
-- v.resize(3) | |
-- resizing members | |
[#0] constructed | |
[#1] constructed | |
[#2] constructed | |
-- v.capacity() = 3 | |
-- v.resize(4) | |
===== END ===== | |
[#2] destroyed | |
[#1] destroyed | |
[#0] destroyed | |
========================= | |
===== Experiment #2 ===== | |
========================= | |
Using push_back. | |
-- v.resize(3) | |
-- pushing elements back | |
[#0] constructed | |
[#1] moved (from element [#0]) | |
[#0] destroyed | |
[#2] constructed | |
[#3] moved (from element [#2]) | |
[#2] destroyed | |
[#4] constructed | |
[#5] moved (from element [#4]) | |
[#4] destroyed | |
-- v.capacity() = 3 | |
-- v.resize(4) | |
===== END ===== | |
[#5] destroyed | |
[#3] destroyed | |
[#1] destroyed | |
========================= | |
===== Experiment #3 ===== | |
========================= | |
Using emplace_back. | |
-- v.resize(4) | |
-- emplacing elements back | |
[#0] constructed | |
[#1] constructed | |
[#2] constructed | |
-- v.capacity() = 3 | |
-- v.resize(4) | |
===== END ===== | |
[#2] destroyed | |
[#1] destroyed | |
[#0] destroyed |
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#include <vector> | |
#include <iostream> | |
int NUM_INSTANCES = 0; | |
class InstanceCounter | |
{ | |
int _instance_number; | |
public: | |
InstanceCounter() | |
{ | |
_instance_number = NUM_INSTANCES++; | |
std::cout << "[#" << _instance_number << "] constructed\n"; | |
} | |
InstanceCounter(const InstanceCounter& rhs) | |
{ | |
_instance_number = NUM_INSTANCES++; | |
std::cout << "[#" << _instance_number << "] copy constructed "; | |
std::cout << "(from element [#" << rhs._instance_number << "])\n"; | |
} | |
// move constructors not available before C++11 | |
#if __cplusplus > 199711L | |
InstanceCounter(InstanceCounter&& rhs) | |
{ | |
_instance_number = NUM_INSTANCES++; | |
std::cout << "[#" << _instance_number << "] moved "; | |
std::cout << "(from element [#" << rhs._instance_number << "])\n"; | |
} | |
#endif | |
~InstanceCounter() | |
{ | |
std::cout << "[#" << _instance_number << "] destroyed\n"; | |
} | |
}; | |
int experiment1(void) | |
{ | |
NUM_INSTANCES = 0; | |
std::cout << "\n=========================\n"; | |
std::cout << "===== Experiment #1 =====\n"; | |
std::cout << "=========================\n"; | |
std::cout << "Resizing and new element construction\n\n"; | |
std::vector<std::vector<InstanceCounter> > v; | |
std::cout << "-- v.resize(3)\n"; | |
v.resize(3); | |
std::cout << "-- resizing members\n"; | |
v[0].resize(1); | |
v[1].resize(1); | |
v[2].resize(1); | |
std::cout << "-- v.capacity() = " << v.capacity() << "\n-- v.resize(4)\n"; | |
v.resize(4); | |
std::cout << "\n===== END =====\n"; | |
return 0; | |
} | |
int experiment2(void) | |
{ | |
NUM_INSTANCES = 0; | |
std::cout << "\n=========================\n"; | |
std::cout << "===== Experiment #2 =====\n"; | |
std::cout << "=========================\n"; | |
std::cout << "Using push_back.\n\n"; | |
std::vector<std::vector<InstanceCounter> > v; | |
std::cout << "-- v.resize(3)\n"; | |
v.resize(3); | |
std::cout << "-- pushing elements back\n"; | |
v[0].push_back(InstanceCounter()); | |
v[1].push_back(InstanceCounter()); | |
v[2].push_back(InstanceCounter()); | |
std::cout << "-- v.capacity() = " << v.capacity() << "\n-- v.resize(4)\n"; | |
v.resize(4); | |
std::cout << "\n===== END =====\n"; | |
return 0; | |
} | |
int experiment3(void) | |
{ | |
// vector.emplace_back not availabe before C++11 | |
#if __cplusplus > 199711L | |
NUM_INSTANCES = 0; | |
std::cout << "\n=========================\n"; | |
std::cout << "===== Experiment #3 =====\n"; | |
std::cout << "=========================\n"; | |
std::cout << "Using emplace_back.\n\n"; | |
std::vector<std::vector<InstanceCounter> > v; | |
std::cout << "-- v.resize(4)\n"; | |
v.resize(3); | |
std::cout << "-- emplacing elements back\n"; | |
v[0].emplace_back(); | |
v[1].emplace_back(); | |
v[2].emplace_back(); | |
std::cout << "-- v.capacity() = " << v.capacity() << "\n-- v.resize(4)\n"; | |
v.resize(4); | |
std::cout << "\n===== END =====\n"; | |
#endif | |
return 0; | |
} | |
int main(int argc, char* argv[]) | |
{ | |
experiment1(); | |
experiment2(); | |
experiment3(); | |
return 0; | |
} |
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