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7.3. Arrays ​

Vala arrays are designed to match most of the C array semantics. Since C arrays, generally, have no explicit length, Vala needs special hints to know what to do. There are several cases for the length of an array, discussed below. For a parameter, a CCode attribute attached to that parameter controls the array's binding. For a return value, the CCode attribute of the method controls the array's binding.

7.3.1. Array Length is Passed as an Argument ​

By default, Vala assumes the first case and does the following transformation:

vala
void foo (double[] array);
double[] foo (float f);
c
void foo(double *array, int array_length);
double *foo(float f, int *array_length);

If the C code does this, there are still two potential mismatches: the order of parameters and the type of the array length. Often, the array length is a size_t or unsigned int. The array_length_pos can move the position of the array's length parameter, see Changing the Position of Parameters. The array_length_type specifies a string with the C type of the array (e.g., size_t).

7.3.2. Array is Null-Terminated ​

The array_null_terminated will assume the array is null terminated, like a string is, and set the array length automatically by iterating over the items in the array. Since Vala always allocates padding in arrays with the final element as null, passing a Vala-declared array in does not involve modifying the array in any way.

7.3.3. Array Length is a Constant Expression ​

The array_length_cexpr can be set to the C expression that populates the array's value. It does not have access to the array, the instance of the object being called, or any other context. It must be a context-free expression.

7.3.4. Array Length is Unknown ​

If the array length is unknown, setting array_length = false in the CCode attribute will cause Vala to set the array's .length property to -1 and not pass the length when used as a parameter.

7.3.5. Array Length is Known by Some Awkward Means ​

This is only applicable for arrays being returned. If the array's length can be determined, but non-trivially, a wrapper function can be included that sets the array's .length property to the correct value. See Array Lengths.