# V2595. MISRA. Array size should be specified explicitly when array declaration uses designated initialization.

This diagnostic rule is based on the software development guidelines developed by MISRA (Motor Industry Software Reliability Association).

This rule is only relevant to C. When designated initialization is used to initialize objects in an array, implicit array size specification may lead to errors. It is because changing object initializers will implicitly resize the array. Specify the number of elements explicitly. This way the array size will be determined accurately and quickly.

    int arr[] = { [0] = 5, [7] = 5, [19] = 5, [3] = 2 };

What if this array size is specified implicitly? Its size is determined by the largest index of initialized objects. When there are many initialized objects, a developer may not always determine the array size correctly. Besides that, deleting or adding initialization of the highest index object can change the size significantly:

    int arr[] = { [0] = 5, [7] = 5, [3] = 2 };

The array size decreased from 20 to 8 elements. The array index may end up out of bounds in the piece where we expect this array with 20 elements.

According to the rule, safe array declaration may look as follows:

    int arr[20] = { [0] = 5, [7] = 5, [19] = 5, [3] = 2 };

This diagnostic is classified as:

MISRA-C-2012-9.5 MISRA-C-2023-9.5