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3.5.2. Reading Values From Arrays

You can also read values from an array the same way you would read the value of a variable. To do so, include the array_name[index_expression] statement as an element in a mathematical expression. For example:

Example 3.15. Using Array Values in Simple Computations

delta = gettimeofday_s() - foo[tid()]

This example assumes that the array foo was built using the construct in Example 3.14, “Associating Timestamps to Process Names” (from Section 3.5.1, “Assigning an Associated Value”). This sets a timestamp that will serve as a reference point, to be used in computing for delta.
The construct in Example 3.15, “Using Array Values in Simple Computations” computes a value for the variable delta by subtracting the associated value of the key tid() from the current gettimeofday_s(). The construct does this by reading the value of tid() from the array. This particular construct is useful for determining the time between two events, such as the start and completion of a read operation.


If the index_expression cannot find the unique key, it returns a value of 0 (for numerical operations, such as Example 3.15, “Using Array Values in Simple Computations”) or a null/empty string value (for string operations) by default.