Assertion (software development): Difference between revisions

Revision as of 06:59, 19 June 2020

Revision as of 09:15, 26 June 2020

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Here, the programmer is aware that <code>[[malloc]]</code> will return a [[Null pointer|<code>NULL</code> pointer]] if memory is not allocated. This is possible: the operating system does not guarantee that every call to <code>malloc</code> will succeed. If an out of memory error occurs the program will immediately abort. Without the assertion, the program would continue running until <code>ptr </code> was dereferenced, and possibly longer, depending on the specific hardware being used. So long as assertions are not disabled, an immediate exit is assured. But if a graceful failure is desired, the program has to handle the failure. For example, a server may have multiple clients, or may hold resources that will not be released cleanly, or it may have uncommitted changes to write to a datastore. In such cases it is better to fail a single transaction than to abort abruptly.

Another error is to rely on side effects of expressions used as arguments of an assertion. One should always keep in mind that assertions might not be executed at all, since their sole purpose is to verify that a condition which should always be true does in fact hold true. Consequently, if the program is considered to be error-free and released, assertions may be disabled and will no longer be evaluated.