C ++ 11为每个循环与多个变量 [英] C++11 for each loop with more than one variable

问题描述

 <$ c $ 
 c> int a [] = {5，6，7，8，9，10}; 
 int b [] = {50，60，70，80，90，100}; 
 
 //交换a和b数组元素
（int i = 0; i< sizeof（a）/ sizeof（a [0]）; i ++）
 { 
a [i] ^ = b [i]; b [i] ^ = a [i]; a [i] ^ = b [i]; 
} 
  

是否有任何方法可以提供多个变量在C ++ 11 for-each循环中：

$ $ $ $ $ $ $ $ $ $ $ $ $ b

解决方案

没有内置的方法来执行此操作。如果您可以使用Boost，那么 boost :: combine 可以同时迭代两个（或多个）范围（，

  for（boost :: tuple< int&; int&> ij：boost :: combine（a，b））{
 int& i = boost :: get（0）（i，j）; 
 int& j = boost :: get（i，j）; 
 // ... 
} 
  

不幸地访问元组中的元素压缩范围的元素非常冗长。 （auto [& i，& j]）使用结构化绑定，C ++ 17将使这个更加可读：

  ：boost :: combine（a，b））{
 // ... 
} 
  

因为你不需要跳出循环或从封闭函数返回，所以你可以使用 boost :: range :: for_each 作为lambda的循环体：

  boost :: range :: for_each（a，b，[]（int& i，int& j）
 {
 // ... 
}）; 
  

I would like to translate the following traditional for loop into a C++11 for-each loop without extra looping constructs:

int a[] = { 5, 6, 7, 8, 9, 10 };
int b[] = { 50, 60, 70, 80, 90, 100 };

// Swap a and b array elements 
for (int i = 0; i < sizeof(a)/sizeof(a[0]); i++)
{
   a[i] ^= b[i]; b[i] ^= a[i]; a[i] ^= b[i];
}

Does there exist any way by which it is possible to provide more than one variable in the C++11 for-each loop like:

for (int i, int j : ...)

解决方案

There is no built-in way to do this. If you can use Boost, boost::combine will work for iterating two (or more) ranges simultaneously (Does boost offer make_zip_range?, How can I iterate over two vectors simultaneously using BOOST_FOREACH?):

for (boost::tuple<int&, int&> ij : boost::combine(a, b)) {
    int& i = boost::get<0>(ij);
    int& j = boost::get<1>(ij);
    // ...
}

Unfortunately accessing the elements within the tuple elements of the zipped range is highly verbose. C++17 will make this much more readable using structured binding:

for (auto [&i, &j] : boost::combine(a, b)) {
    // ...
}

Since you don't need to break out of the loop or return from the enclosing function, you could use boost::range::for_each with the body of your loop as a lambda:

boost::range::for_each(a, b, [](int& i, int& j)
{
    // ...
});

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