<1>auto ，initializer_list<T>,auto指向函数指针的简易，和typdef 定义的类型执行函数指针有多复杂。
#include <iostream>
#include <initializer_list>
#include <string>
using namespace std; template <typename T>
T sum(initializer_list<T> rh)
{
T val;
for(auto p= rh.begin();p!=rh.end();p++)
{
val+= *p;
}
return val;
} int main()
{
// use init list
cout << sum({,,,,}) <<endl;
cout << sum({1.0,2.0,3.1,4.0,5.0}) <<endl; //
cout << "use auto to point the function sum" <<endl;
auto dadd_func = sum<double>;
auto iadd_func = sum<int>;
auto tadd_func = sum<string>;
cout << dadd_func({,,,}) <<endl;
cout << iadd_func({,,,,}) <<endl;
cout << tadd_func({"houdini","maya","json"}) <<endl; cout << "\nuse the typedef to pointer\n";
typedef int (*td_int_sum)(initializer_list<int> rh);
typedef string (*td_str_sum)(initializer_list<string> rh);
td_int_sum int_add = sum<int>;
td_str_sum str_add = sum<string>;
cout << int_add({,,,,,}) <<endl;
cout << str_add({"s1","s2","s5"}) << endl; return ;
}
<2>funcional,std::generate,std::count_if
#include <iostream>
#include <math.h>
#include <vector>
#include <algorithm>
#include <functional> using namespace std; double square(double x){return x*x;} int main()
{
vector <int> vars(); generate(vars.begin(),vars.end(),std::rand);
for_each(vars.begin(),vars.end(),[](int v){cout << v <<endl;}); // lambda can transfer local variable
int sum = ;
for_each(vars.begin(),vars.end(),[&sum](int v){sum+=v;});
cout << "the sum is " << sum <<endl; // <100 num
cout << "get <100 numbers" <<endl;
cout << count_if(vars.begin(),vars.end(),[](int v){ return v<;}) <<endl; // functional
function<double(double)> ef1 = square;
cout << ef1() <<endl; // function<void(int var)> ef2 = [](int val){cout << val <<endl;};
ef2(); // return ;
}
<3> remove_if,vector,min_element,max_element
include <iostream>
#include <algorithm>
#include <vector>
#include <string>
using namespace std; void cppRemove_if()
{
cout << "====cppRemove_if====\n";
int myInts[]{,,,,,,,}; // 1 2 3 4 5 6 7 8
int *pbegin = myInts;
int *pend = myInts + sizeof(myInts)/ sizeof(int);
pend = remove_if(pbegin,pend,
[](const int &val)->bool{return val% == ;});//2 4 5 8 ? ? ? ?
for (int* p=pbegin; p!=pend; ++p)
cout << ' ' << *p;
cout << "\n";
cout << "====cppRemove_if====\n"; } int main()
{ vector<int> va{,,,,,}; // find, if not find elements,will return last *iter;
auto va_find2 = find(va.begin(),va.end(),);
auto va_find2e = find_if(va.begin(),va.end(),[](const int &x){return x==;});
cout << *va_find2 <<endl;
cout << *va_find2e <<endl; cout << *min_element(va.begin(),va.end()) <<endl;
cout << *max_element(va.begin(),va.end()) <<endl; auto min_max = minmax_element(va.begin(),va.end());
cout << "min val:" <<*(min_max.first)<<endl;
cout << "max val:" <<*(min_max.second)<<endl; cout << "remove the second elements \n";
va.erase(va.begin()+,va.begin()+);
for_each(va.begin(),va.end(),[](const int &x){cout << x <<endl;}); cout << "remove by condition <5 \n";
va.erase(remove_if(va.begin(),va.end(),[](int x){return x <;}),va.end());
for_each(va.begin(),va.end(),[](const int &x){cout << x <<endl;}); cppRemove_if();
return ;
}
<4>binary_search,sort更加详细的用法:
#include <iostream>
#include <algorithm>
#include <vector>
#include <functional>
using namespace std; template <typename T1>
void ShowIntArray(const T1 begin, const T1 end)
{
for_each(begin,end,[](const int &x){cout << x <<" "; });
cout << "\n";
}
template <typename T>
void ShowSTLArray(const T&cont)
{
auto iter = cont.begin();
auto end = cont.end();
for(;iter!=end;iter++)
{
cout << *iter <<" ";
}
cout <<endl;
}; void cpp_sort()
{
int a[]= {,,,,,};
int *begin = a;
int *end = a + ; cout << "before sort:\n";
ShowIntArray(begin, end); sort(begin,end);
cout << "after sort:\n";
ShowIntArray(begin, end); cout << "from large to small:\n";
sort(begin,end,[](const int &x,const int &y){return x>y;});
ShowIntArray(begin, end); cout << "from small to large use less<int>():\n";
sort(begin,end,less<int>());
ShowIntArray(begin, end); cout << "from large to small use greater<int>():\n";
sort(begin,end,greater<int>());
ShowIntArray(begin, end); vector<string> vecStr{"Got","cool","features"};
cout << "sort the sting array:\n";
ShowSTLArray(vecStr);
auto strCmp = [](string &a,string &b)
{
return a.length() > b.length();
};
cout << "sort the array results:\n";
sort(vecStr.begin(),vecStr.end(),strCmp);
ShowSTLArray(vecStr); } void cpp_binary_search()
{ cout << "=======search 01:==========\n";
std::vector<int> haystack {, , , , };
std::vector<int> needles {, , };
sort(haystack.begin(),haystack.end());
for (auto needle : needles)
{
cout << "Searching for " << needle << '\n';
if (binary_search(haystack.begin(), haystack.end(), needle))
{ cout << "Found " << needle << '\n';
}
else
{
cout << "no dice!\n";
}
}
cout << "=======search 01:==========\n"; std::vector<int> haystack2 {, , , , ,,,};
sort(haystack2.begin(),haystack2.end(),[](int &x,int &y){return x<y;});
ShowSTLArray(haystack2); auto func =[](int i,int j)->bool{cout<< "i:" << i; cout << " j:"<<j;cout<<"\n";return (i<j);};
if (binary_search(haystack2.begin(),haystack2.end(),,func))
{
cout << "found 5" <<endl;
} } int main()
{
//cpp_sort();
cpp_binary_search();
return ;
}
binarySearch结果:
Sort结果:
<5> 线程大法
(1) hello world thread:
#include <iostream>
#include <thread>
#include <memory>
using namespace std; void thread_task()
{
cout << "thread hello world\n";
} int main()
{
shared_ptr<thread> t(new thread(thread_task));
t->join(); return ;
}
(2)带参数的函数(bind方法，直接使用thread构造也可以)
void thread_parm(const int &n,const string& name)
{
for(int i=;i<n;i++)
{
cout << name <<":thread loop in " << i <<endl;
}
} void withParam()
{
thread t0(thread_parm,,"houdini");
thread t1(bind(thread_parm,,"maya"));
t0.join();
t1.join();
} int main()
{
withParam();
return ;
}
(3)成员对象函数执行在线程中（也可以作用到智能指针对象）
class HelloObject
{
public:
void sayHello(const string& name,int n)
{
for(int i=;i<n;i++)
{
cout << name << " thread: " << i <<endl;
}
}
}; void objectFunction()
{
HelloObject obj;
thread t(&HelloObject::sayHello,&obj,"Json",);
t.join(); // work with shared_ptr
shared_ptr<HelloObject> objPtr(new HelloObject());
thread tptr(&HelloObject::sayHello,objPtr,"Houdini",);
tptr.join();
} int main()
{
objectFunction();
return ;
}
(4)传递引用，头文件functional，std::ref()
class FuncObj
{
public:
void operator()()const
{
cout << this <<endl;
}
};
void passRef()
{
auto obj = FuncObj();
obj(); //pass by value
cout << "thread will pass by value\n";
thread t1(obj);
t1.join(); //pass by ref
cout << "thread will pass by ref\n";
thread t2(ref(obj));
t2.join(); } int main()
{
passRef();
return ;
}
结果:
0x22fdff
thread will pass by value
0x7c6150
thread will pass by ref
0x22fdff
普通的函数也可以
void increment(int &value)
{
value++ ;
cout << "value :" << value <<endl; }
void passRef2()
{
int a = ;
thread t(increment,ref(a));
t.join();
} int main()
{
passRef2();
return ;
}
(5)基本功能:
匿名函数:get_id() 区分线程
void lambdaTest()
{
vector <thread> threads;
for(int i=;i<;i++)
{
threads.emplace_back(thread([](){cout << "thread id " << this_thread::get_id() << endl;}));
} for(auto &t : threads)
{
t.join();
}
} int main()
{
lambdaTest();
return ;
}
总线程数:
cout << thread::hardware_concurrency() <<endl;
(6)异常与线程
标准处理方法
struct Counter2
{
int value;
Counter2():value(){}
void increment()
{
++value;
}
void decrement()
{
if(value == )
{
throw string("value cannot be less than 0");
} --value;
}
}; struct Wrapper
{
Counter2 ct;
mutex m; void increment()
{ }
void decrement()
{
m.lock();
try
{
ct.decrement();
}
catch (const string &e)
{
m.unlock();
cout << e <<endl;
throw e;
} m.unlock();
}
}; void exceptionLock()
{
Wrapper wap;
wap.ct.value = ; vector<thread> threads;
for(int i=;i<;i++)
{
threads.emplace_back(thread([&wap](){
wap.decrement(); }));
}
for(auto &t:threads)
{
t.join();
}
cout << wap.ct.value << endl;
}
(7)模仿Inter TBB parallel_for
串行时间:87
并行时间:19
struct BlockRange
{
BlockRange():begin(),end()
{ }
int begin;
int end;
}; class ApplyFoo
{
public:
ApplyFoo(vector<int> *data):mData(data)
{
}
void operator()(const BlockRange &range)const
{
for(int i=range.begin;i<range.end;i++)
{
(*mData)[i] += ;
}
}
private:
vector<int> *mData;
}; template <typename T>
void parallel_for(const T &body,int size,int begin)
{
auto nThreads = thread::hardware_concurrency();
auto nValuesSize = size;
auto perBlockSize =nValuesSize / nThreads;
if(nValuesSize < nThreads)
{
BlockRange range;
range.begin = begin;
range.end = nValuesSize;
body(range);
return;
}
// building blocks
vector<BlockRange> blocks;
int index = begin;
while(index <= nValuesSize)
{
BlockRange range;
range.begin = index;
range.end = index+ perBlockSize;
blocks.push_back(range);
index += (perBlockSize) ;
}
// fix last block end size;
blocks[blocks.size()-].end = nValuesSize;
// thread pool to run
typedef shared_ptr<thread> thread_ptr;
vector<thread_ptr> pools;
for(BlockRange&r:blocks)
{
pools.emplace_back(new thread(body,r));
}
for(auto &t:pools)
{
t->join();
} } void parallel()
{
vector<int> values();
fill(values.begin(),values.end(),); double start,end,cost;
start=clock();
parallel_for(ApplyFoo(&values),values.size(),);
end= clock();
cost = end -start;
cout << "parallel for cost time:" << cost <<endl; }
void serial()
{
vector<int> values();
fill(values.begin(),values.end(),); double start,end,cost;
start=clock();
for(int i=;i<values.size();i++)
{
values[i] += ;
}
end= clock();
cost = end -start;
cout << "serial for cost time:" << cost <<endl;
} int main()
{ parallel();
serial();
return ;
}
并行accumulation:
10亿个元素相加:简直他妈的快飞起来了。
串行时间:13063
并行时间:1023
#include <vector>
#include <time.h>
#include <iostream>
#include <thread>
#include <algorithm>
using namespace std; struct BlockRange
{
BlockRange():begin(),end(),id()
{ }
int begin;
int end;
int id;
}; class ApplyFoo
{
public:
ApplyFoo(vector<int> *data):mData(data)
{
}
void operator()(const BlockRange &range,vector<int> *des)const
{
auto value = int();
for(int i=range.begin;i<range.end;i++)
{
value +=(*mData)[i];
}
(*des)[range.id] = value;
}
private:
vector<int> *mData; }; template <typename retType,typename T>
retType parallel_add(const T &body,int size,int begin)
{
vector<retType> partial_accum;
auto nThreads = thread::hardware_concurrency();
auto nValuesSize = size;
auto perBlockSize =nValuesSize / nThreads;
if(nValuesSize < nThreads)
{
partial_accum.resize();
BlockRange range;
range.begin = begin;
range.end = nValuesSize;
range.id = ;
body(range,&partial_accum);
return accumulate(partial_accum.begin(),partial_accum.end(),retType());
}
// building blocks
vector<BlockRange> blocks;
int index = begin;
int blockId = ;
while(index <= nValuesSize)
{
BlockRange range;
range.begin = index;
range.end = index+ perBlockSize;
range.id = blockId;
blocks.push_back(range);
index += (perBlockSize) ;
blockId += ;
}
partial_accum.resize(blocks.size()); // fix last block end size;
blocks[blocks.size()-].end = nValuesSize;
// thread pool to run
typedef shared_ptr<thread> thread_ptr;
vector<thread_ptr> pools; for(BlockRange&r:blocks)
{
pools.emplace_back(new thread(body,r,&partial_accum));
}
for(auto &t:pools)
{
t->join();
} return accumulate(partial_accum.begin(),partial_accum.end(),retType()); } void parallel()
{
vector<int> values();
fill(values.begin(),values.end(),); double start,end,cost;
start=clock();
cout << "get the result :" <<parallel_add<int>(ApplyFoo(&values),values.size(),) <<endl;
end= clock();
cost = end -start;
cout << "parallel for cost time:" << cost <<endl;
} void serial()
{
vector<int> values();
fill(values.begin(),values.end(),); double start,end,cost;
start=clock();
cout << "get the result :" <<accumulate(values.begin(),values.end(),) <<endl;
end= clock();
cost = end -start;
cout << "parallel for cost time:" << cost <<endl;
} int main()
{ parallel();
//serial();
return ;
}
<n> boost bind
#include <boost/bind.hpp>
#include <boost/shared_ptr.hpp> #include <iostream>
using namespace std;
void dprint(int x,int y)
{
cout << x << " " <<y <<endl;
} class Bind_test
{
public:
void setData(int x,int y)
{
_x = x;
_y = y;
}
void printData()
{
cout << _x << " " <<_y <<endl;
}
private:
int _x;
int _y; }; void increnum(int &dg)
{
dg++;
} int main()
{
boost::bind(&dprint,,)(); // 5,5
boost::bind(&dprint,,_1)(); // 3, 5
boost::bind(&dprint,_1,_1)(); // 2, 2
boost::bind(&dprint,_1,_2)(,); // 1, 2
boost::bind(&dprint,_2,_1)(,); // 2, 1 ->函数参数对掉 cout << "\nbind the class function\n";
boost::shared_ptr<Bind_test> bclass(new Bind_test);
boost::bind(&Bind_test::setData,bclass,,)();
bclass->printData(); Bind_test *bclass_02 = new Bind_test;
boost::bind(&Bind_test::setData,bclass_02,,)();
bclass_02->printData(); // 2 ,3
delete bclass_02; Bind_test bclass_03;
boost::bind(&Bind_test::setData,&bclass_03,,)();
bclass_03.printData(); // 4 ,5
boost::bind(&Bind_test::setData,&bclass_03,_1,_1)();
bclass_03.printData(); // 9 ,9
boost::bind(&Bind_test::setData,&bclass_03,_1,_2)(,);
bclass_03.printData(); // 9 ,10 int dgNum = ;
boost::bind(&increnum,boost::ref(dgNum))(); // 类似C++11 Thread 里要传递引用std::ref(x)
cout << dgNum <<endl; cin.get();
return ;
}
额外的:
static_assert 编译时候assertions
下面将输出:hello \n no
cout << R"(hello \n no)" <<endl;
。