如何用STL重構這段代碼？

Question

這裏是我運動代碼.. 書的問題是重構這個代碼模板（與STL）

我發現了一些書和谷歌，但我不明白這一點

你能告訴我請舉例？ ？

int SumInt(const int* a, int count) { 
    int result = 0; 
    for (int i = 0; i < count; ++i) { 
    result += a[i]; 
    } 
    return result; 
} 

float SumFloat(const float* a, int count) { 
    float result = 0; 
    for (int i = 0; i < count; ++i) { 
    result += a[i]; 
    } 
    return result; 
} 
void main() { 
    int intVals[] = {0, 1, 2}; 
    float floatVals[] = {0.F, 1.F, 2.F}; 

    int intTotal = SumInt(intVals, 3); 
    float floatTotal = SumFloat(floatVals, 3); 

.... 
} 

Answer 1

您使用這樣的模板。還可以閱讀他們：http://www.cplusplus.com/doc/oldtutorial/templates/

template<typename T> 
T doSomething(const T a, int count) 
{ 
    // do your stuff 

} 

你使用這樣的：

int w = 1; 
doSomething(w, 1); 

您與int在這種情況下更換T

Answer 2

您可以使用std::accumulate：

int intTotal = std::accumulate(std::begin(intVals), std::end(intVals), 0); 
float floatTotal = std::accumulate(std::begin(floatVals), std::end(floatVals), 0.0F); 

Answer 3

在這個例子中，你可以用一個模板Sum同時取代SumInt和SumFloat如下：

template <typename T> int Sum(const T* a, int count) { 
    T result = 0; 
    for (int i = 0; i < count; ++i) { 
     result += a[i]; 
    } 
    return result; 
} 

然後在你的main()，你可以叫

int intTotal = Sum(intVals, 3); 
float floatTotal = Sum(floatVals, 3); 

和編譯器會調用要麼int或float版本取決於您提供給Sum的參數類型。

Answer 4

這裏，我們去（你和一個簡單的模板（...）函數）：

template <typename T> 
T sum(const T* a, size_t count) { 
    T result = 0; 
    for (size_t i = 0; i < count; ++i) { 
     result += a[i]; 
    } 
    return result; 
} 

int main() { 
    const int intVals[] = { 0, 1, 2 }; 
    const float floatVals[] = { 0.F, 1.F, 2.F }; 

    const int intTotal = sum(intVals, 3); 
    const float floatTotal = sum(floatVals, 3); 

    std::cout << "float total: " << intTotal << std::endl; 
    std::cout << "int total: " << floatTotal << std::endl; 
} 

我喜歡std::accumulate，雖然：

int main() { 
    const auto intVals = { 0, 1, 2 }; 
    const auto floatVals = { 0.F, 1.F, 2.F }; 

    const auto intTotal = std::accumulate(intVals.begin(), intVals.end(), 0); 
    const auto floatTotal = std::accumulate(floatVals.begin(), floatVals.end(), 0.0F); 

    std::cout << "float total: " << intTotal << std::endl; 
    std::cout << "int total: " << floatTotal << std::endl; 
} 

Answer 5

的實現涉及模板參數和使用STL（C++標準庫）的：

#include <iostream> 
#include <vector> 
#include <cstddef> 

template <typename T> 
T Sum(const std::vector<T>& a) { 
    T result = 0; 
    for (size_t i = 0; i < a.size(); ++i) { 
     result += a[i]; 
    } 
    return result; 
} 


int main() { 
    std::vector<int> intVals {0, 1, 2}; 
    std::vector<float> floatVals {0.F, 1.F, 2.F}; 

    int intTotal = Sum(intVals); 
    float floatTotal = Sum(floatVals); 

    std::cout << intTotal << std::endl; 
    std::cout << floatTotal << std::endl; 
} 

參見Live Demo