3.6. 练习

You can buy solutions to all exercises in this book as a ZIP file.

• 简化以下程序，将函数对象 divide_by 转换为一个函数，并将 for 循环替换为用一个标准的 C++ 算法来输出数据：

#include <algorithm> 
#include <functional> 
#include <vector> 
#include <iostream> 
 
class divide_by 
  : public std::binary_function<int, int, int> 
{ 
public: 
  int operator()(int n, int div) const 
  { 
    return n / div; 
  } 
}; 
 
int main() 
{ 
  std::vector<int> numbers; 
  numbers.push_back(10); 
  numbers.push_back(20); 
  numbers.push_back(30); 
 
  std::transform(numbers.begin(), numbers.end(), numbers.begin(), std::bind2nd(divide_by(), 2)); 
 
  for (std::vector<int>::iterator it = numbers.begin(); it != numbers.end(); ++it) 
    std::cout << *it << std::endl; 
} 

• 下载源代码
  • 简化以下程序，将两个 for 循环都替换为标准的 C++ 算法：

#include <string> 
#include <vector> 
#include <iostream> 
 
int main() 
{ 
  std::vector<std::string> strings; 
  strings.push_back("Boost"); 
  strings.push_back("C++"); 
  strings.push_back("Libraries"); 
 
  std::vector<int> sizes; 
 
  for (std::vector<std::string>::iterator it = strings.begin(); it != strings.end(); ++it) 
    sizes.push_back(it->size()); 
 
  for (std::vector<int>::iterator it = sizes.begin(); it != sizes.end(); ++it) 
    std::cout << *it << std::endl; 
} 

• 下载源代码
  • 简化以下程序，修改变量 processors 的类型，并将 for 循环替换为标准的 C++ 算法：

#include <vector> 
#include <iostream> 
#include <cstdlib> 
#include <cstring> 
 
int main() 
{ 
  std::vector<int(*)(const char*)> processors; 
  processors.push_back(std::atoi); 
  processors.push_back(reinterpret_cast<int(*)(const char*)>(std::strlen)); 
 
  const char data[] = "1.23"; 
 
  for (std::vector<int(*)(const char*)>::iterator it = processors.begin(); it != processors.end(); ++it) 
    std::cout << (*it)(data) << std::endl; 
} 

• 下载源代码