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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 [AA. Bibliography#ISO-ISO/IEC 9899-:2011] states:

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

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

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.

Exceptions

ARR02-C-EX1: STR11-C. Do not specify the bound of a character array initialized with a string literal is a specific exception to this recommendation; it requires that the bound of a character array initialized with a string literal is unspecified.

Risk Assessment

Automated Detection

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Related Guidelines

Key here (explains table format and definitions)

Bibliography

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