CODEWITHSUNDEEP
c++arraystypescasting
BreezyMain
BreezyMain

Reputation: 163

Why the element of a Two-dimensional array in range based for loop is T* instead of T (*)[n]?

There is my code

int array[3][4] = {
  {1, 2, 3},
  {4, 5, 6},
  {7, 8, 9}
};

for (auto line : array)
  // something

Why the type of line is int * instead of int (*)[4]?

I have looked for reference about the range-based for loop, and I'm using C++ 11, so the corresponding source code is

{
  auto && __range = range_expression ;
  for (auto __begin = begin_expr, __end = end_expr; __begin != __end; ++__begin) {
    range_declaration = *__begin;
  loop_statement
}

According to the first item of the Explanation:

If range_expression is an expression of array type, then begin_expr is __range

so there is a satement __begin = range_expression, and it equal to auto line = array.
and then the type of line is int (*)[4], but in fact it's int *?

Why? Could anybody help me?

Upvotes: 2

Views: 67

Answers (1)

nickelpro
nickelpro

Reputation: 2917

In your example __begin is of type int(*)[4]

range_declaration is the dereferenced value of __begin, therefore in your example range_declaration is of type int*.

In your example, the line variable is the range_declaration.

If we remove the syntactic sugar, your code looks like this:

int array[3][4] = {{1, 2, 3, 0}, {4, 5, 6, 0}, {7, 8, 9, 0}};
{
  int (&__range)[3][4] = array;
  int (*__begin)[4] = __range;
  int (*__end)[4] = __range + 3L;
  for(; __begin != __end; ++__begin) {
    int * line = *__begin;
  }
}

Upvotes: 2

Related Questions