[转]C++模板详解

C++模板通常有两种形式：函数模板和类模板。函数模板针对：参数类型不同的函数；类模板针对：数据成员和成员函数类型不同的类。
模板的声明或定义只能在全局，命名空间或类范围内进行，不能在局部、函数内进行。

函数模板

template <class 形参名,class 形参名,……>返回类型 函数名(参数列表){
    //函数体
}//class可用typename代替
//例如：
template <class T> void swap(T&a, T&b){}

类模板

template<class 形参名, class 形参名,……> class 类名{
//...
};
//例如：
template<class T>class A{
public: 
    T a;
    T b;
    T hy(T c, T& d);
};

实例展示

template<typename Iterator, typename T> struct accumulate_block {
void operator()(Iterator first, Iterator last, T& result) {
    result = std::accumulate(first, last, result);
}
};//类模板：accumulate_block

template<typename Iterator, typename T>
T parallel_accumulate(Iterator first, Iterator last, T init) {
    unsigned long const length = std::distance(first, last);

    if(!length) return init;

    unsigned long const min_per_thread=25;
    unsigned long const max_threads = (length+min_per_thread-1)/min_per_thread;

    unsigned long const hardware_threads = std::thread::hardware_concurrency();

    unsigned long const num_threads = std::min(hardware_threads!=0?hardware_threads:2,max_threads);

    unsigned long const block_size = length/num_threads;

    std::vector<T> results(num_threads);
    std::vector<std::thread> threads(num_threads-1);

    Iterator block_start = first;
    for(unsigned long i = 0; i < (num_threads-1); ++i) {
        Iterator block_end = block_start;
        std::advance(block_end, block_size);
        threads[i] = std::thread(
            accumulate_block<Iterator, T>(), block_start, block_end, std::ref(results[i]));
        block_start = block_end;
    }
    accumulate_block<Iterator, T>()(
    block_start, last, results[num_threads-1]);
    std::for_each(threads.begin(), threads.end(), std::mem_fn(&std::thread::join));

    return std::accumulate(results.begin(), results.end(), init);
}//函数模板：T parallel_accumulate(Iterator first, Iterator last, T init);