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The size implied by an initialization literal is usually specified by the number of elements,

int array[] = {1, 2, 3}; /* 3-element array */

but it is also possible to use designators to initialize array elements in a noncontiguous fashion. Subclause 6.7.9, Example 12, of the C Standard [ISO/AA. Bibliography#ISO-IEC 9899:-2011] states:

Space can be "allocated" from both ends of an array by using a single designator:

int a[MAX] = { 1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0 };

Code Block

In the above, if MAX is greater than ten, there will be some zero-valued elements in the middle; if it is less than ten, some of the values provided by the first five initializers will be overridden by the second five.

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int a[3] = {1, 2, 3, 4};

The size of the array a is 3, although the size of the initialization is 4. The last element of the initialization (4) is ignored. Most compilers will diagnose this error.

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int a[] = {1, 2, 3, 4};

Compliant Solution

This compliant solution explicitly specifies the array bound:

int a[4] = {1, 2, 3, 4};

Explicitly specifying the array bound, although it is implicitly defined by an initializer, allows a compiler or other static analysis tool to issue a diagnostic if these values do not agree.

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Bibliography

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