MISRA C:2012 Rule 9.3

Arrays shall not be partially initialized

Description

Rule Definition

Arrays shall not be partially initialized¹ .

Rationale

Providing an explicit initialization for each array element makes it clear that every element has been considered.

Polyspace Implementation

The checker reports a violation of this rule if an array is partially initialized at declaration. The checker allows initialization of all values using the shorthand notation {0}, for instance:

float dat2[3*3] = {0};

Troubleshooting

If you expect a rule violation but do not see it, refer to Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

Partial and Complete Initializations

void func(void) {
    int x[3] = {0,1,2};               /* Compliant */
    int y[3] = {0,1};                 /* Non-compliant */
    int z[3] = {0};                   /* Compliant - exception */
    int a[30] = {[1] = 1,[15]=1};     /* Compliant - exception */
    int b[30] = {[1] = 1, 1};         /* Non-compliant */
    char c[20] = "Hello World";       /* Compliant - exception */
}

In this example, the rule is not violated when each array element is explicitly initialized.

The rule is violated when some elements of the array are implicitly initialized. Exceptions include the following:

• The initializer has the form {0}, which initializes all elements to zero.

• The array initializer consists only of designated initializers. Typically, you use this approach for sparse initialization.

• The array is initialized using a string literal.

Check Information

Group: Initialization

Category: Required

AGC Category: Readability

Version History

Introduced in R2014b

R2024a: Partial initialization of structures no longer flagged

The rule checker no longer reports a violation on structures that have been partially initialized as the rule is specific to arrays.

R2024a: Partially initialized arrays due to designated initializer issues flagged

In R2024a, the rule checker now more accurately checks for partially initialized arrays due to gaps in the initialization caused by using designated initializers. For example:

uint32_t example1[4] = { [1] = 1, 2, 3 };       // Noncompliant
uint32_t example2[4] = { [0] = 1, [2] = 3, 4 }; // Noncompliant
uint32_t example3[4] = { [0] = 1, [1] = 0, [2] = 3, 4 }; // Compliant

R2023a: Incorrect shorthand notation for array initialization flagged

The rule checker reports a violation when an array is initialized with an incorrect shorthand notation such as {0.0}, {0U} or {} (instead of the usual {0}).