7.4.2. Initializing an array in a Declaration with an Initializer List

The elements of an array also can be initialized in the array declaration by following the array name with an equals sign and a brace-delimited comma-separated list of initializers. The program in Fig. 7.4 uses an initializer list to initialize an integer array with five values (line 11) and prints the array in tabular format (lines 13–17).

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 1   // Fig. 7.4: fig07_04.cpp
 2   // Initializing an array in a declaration.
 3   #include <iostream>
 4   #include <iomanip>
 5   #include <array>
 6   using namespace std;
 7
 8   int main()
 9   {
10      // use list initializer to initialize array n
11      array< int, 5 > n = { 32, 27, 64, 18, 95 };  
12
13      cout << "Element" << setw( 13 ) << "Value" << endl;
14
15      // output each array element's value
16      for ( size_t i = 0; i < n.size(); ++i )
17         cout << setw( 7 ) << i << setw( 13 ) << n[ i ] << endl;
18   } // end main

Element        Value
      0           32
      1           27
      2           64
      3           18
      4           95

Fig. 7.4. Initializing an array in a declaration.

If there are fewer initializers than array elements, the remaining array elements are initialized to zero. For example, the elements of array n in Fig. 7.3 could have been initialized to zero with the declaration

array< int, 5 > n = {}; // initialize elements of array n to 0

which initializes the elements to zero, because there are fewer initializers (none in this case) than array elements. This technique can be used only in the array’s declaration, whereas the initialization technique shown in Fig. 7.3 can be used repeatedly during program execution to “reinitialize” an array’s elements.

If the array size and an initializer list are specified in an array declaration, the number of initializers must be less than or equal to the array size. The array declaration

array< int, 5 > n = { 32, 27, 64, 18, 95, 14 };

causes a compilation error, because there are six initializers and only five array elements.

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