Dev C++ Char Array
If pointer ptr was pointer to char then, the address between ptr and ptr + 1 would have differed by 1 byte since size of a character is 1 byte. Example 1: C Pointers and Arrays. C Program to display address of elements of an array using both array and pointers. In both cases, the array of characters myword is declared with a size of 6 elements of type char: the 5 characters that compose the word 'Hello', plus a final null character ('0'), which specifies the end of the sequence and that, in the second case, when using double quotes (') it is appended automatically.
-->An array is a sequence of objects of the same type that occupy a contiguous area of memory. Traditional C-style arrays are the source of many bugs, but are still common, especially in older code bases. In modern C++, we strongly recommend using std::vector or std::array instead of C-style arrays described in this section. Both of these standard library types store their elements as a contiguous block of memory but provide much greater type safety along with iterators that are guaranteed to point to a valid location within the sequence. For more information, see Containers (Modern C++).
Stack declarations
In a C++ array declaration, the array size is specified after the variable name, not after the type name as in some other languages. The following example declares an array of 1000 doubles to be allocated on the stack. The number of elements must be supplied as an integer literal or else as a constant expression because the compiler has to know how much stack space to allocate; it cannot use a value computed at run-time. Each element in the array is assigned a default value of 0. If you do not assign a default value, each element will initially contain whatever random values happen to be at that location.
The first element in the array is the 0th element, and the last element is the (n-1) element, where n is the number of elements the array can contain. The number of elements in the declaration must be of an integral type and must be greater than 0. It is your responsibility to ensure that your program never passes a value to the subscript operator that is greater than (size - 1).
A zero-sized array is legal only when the array is the last field in a struct or union and when the Microsoft extensions (/Ze) are enabled.
Stack-based arrays are faster to allocate and access than heap-based arrays, but the number of elements can't be so large that it uses up too much stack memory. How much is too much depends on your program. You can use profiling tools to determine whether an array is too large.
Heap declarations
If you require an array that is too large to be allocated on the stack, or whose size cannot be known at compile time, you can allocate it on the heap with a new[] expression. The operator returns a pointer to the first element. You can use the subscript operator with the pointer variable just as with a stack-based array. You can also use pointer arithmetic to move the pointer to any arbitrary elements in the array. It is your responsibility to ensure that:
- you always keep a copy of the original pointer address so that you can delete the memory when you no longer need the array.
- you do not increment or decrement the pointer address past the array bounds.
The following example shows how to define an array on the heap at run time, and how to access the array elements using the subscript operator or by using pointer arithmetic:
Initializing arrays
You can initialize an array in a loop, one element at a time, or in a single statement. The contents of the following two arrays are identical:
Passing arrays to functions
When an array is passed to a function, it is passed as a pointer to the first element. This is true for both stack-based and heap-based arrays. The pointer contains no additional size or type information. This behavior is called pointer decay. When you pass an array to a function, you must always specify the number of elements in a separate parameter. This behavior also implies that the array elements are not copied when the array is passed to a function. To prevent the function from modifying the elements, specify the parameter as a pointer to const elements.
The following example shows a function that accepts an array and a length. The pointer points to the original array, not a copy. Because the parameter is not const, the function can modify the array elements.
Declare the array as const to make it read-only within the function block:
The same function can also be declared in these ways, with no change in behavior. The array is still passed as a pointer to the first element:
Multidimensional arrays
Arrays constructed from other arrays are multidimensional arrays. These multidimensional arrays are specified by placing multiple bracketed constant expressions in sequence. For example, consider this declaration:
It specifies an array of type int, conceptually arranged in a two-dimensional matrix of five rows and seven columns, as shown in the following figure:
Conceptual layout of a multi-dimensional array
In declarations of multidimensioned arrays that have an initializer list (as described in Initializers), the constant expression that specifies the bounds for the first dimension can be omitted. For example:
The preceding declaration defines an array that is three rows by four columns. The rows represent factories and the columns represent markets to which the factories ship. The values are the transportation costs from the factories to the markets. The first dimension of the array is left out, but the compiler fills it in by examining the initializer.
Use of the indirection operator (*) on an n-dimensional array type yields an n-1 dimensional array. If n is 1, a scalar (or array element) is yielded.
C++ arrays are stored in row-major order. Row-major order means the last subscript varies the fastest.
Example
The technique of omitting the bounds specification for the first dimension of a multidimensional array can also be used in function declarations as follows:
The function FindMinToMkt is written such that adding new factories does not require any code changes, just a recompilation.
Initializing Arrays
If a class has a constructor, arrays of that class are initialized by a constructor. If there are fewer items in the initializer list than elements in the array, the default constructor is used for the remaining elements. If no default constructor is defined for the class, the initializer list must be complete — that is, there must be one initializer for each element in the array.
Consider the Point class that defines two constructors:
The first element of aPoint is constructed using the constructor Point( int, int ); the remaining two elements are constructed using the default constructor.
Static member arrays (whether const or not) can be initialized in their definitions (outside the class declaration). For example:
Accessing array elements
You can access individual elements of an array by using the array subscript operator ([ ]). If a one-dimensional array is used in an expression that has no subscript, the array name evaluates to a pointer to the first element in the array.
When you use multidimensional arrays, you can use various combinations in expressions.
In the preceding code, multi is a three-dimensional array of type double. The p2multi pointer points to an array of type double of size three. In this example, the array is used with one, two, and three subscripts. Although it is more common to specify all subscripts, as in the cout statement, it is sometimes useful to select a specific subset of array elements, as shown in the statements that follow cout.
Overloading subscript operator
Like other operators, the subscript operator ([]) can be redefined by the user. The default behavior of the subscript operator, if not overloaded, is to combine the array name and the subscript using the following method:
*((array_name) + (subscript))
As in all addition that involves pointer types, scaling is performed automatically to adjust for the size of the type. Therefore, the resultant value is not n bytes from the origin of array-name; rather, it is the nth element of the array. For more information about this conversion, see Additive operators.
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Similarly, for multidimensional arrays, the address is derived using the following method:
((array_name) + (subscript1 * max2 * max3 * .. * maxn) + (subscript2 * max3 * .. * maxn) + .. + subscriptn))
Arrays in Expressions
When an identifier of an array type appears in an expression other than sizeof, address-of (&), or initialization of a reference, it is converted to a pointer to the first array element. For example:
The pointer psz points to the first element of the array szError1. Arrays, unlike pointers, are not modifiable l-values. Therefore, the following assignment is illegal: