Duplicate Key in Associative List (Alist)

Duplicate keys in associative lists can lead to non-unique keys being mistaken for an error.


A duplicate key entry -- if the alist is designed properly -- could be used as a constant time replace function. However, duplicate key entries could be inserted by mistake. Because of this ambiguity, duplicate key entries in an association list are not recommended and should not be allowed.


The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The following code adds data to a list and then attempts to sort the data.

alist = []
while (foo()): #now assume there is a string data with a key basename

Since basename is not necessarily unique, this may not sort how one would like it to be.

See Also

Comprehensive Categorization: Poor Coding Practices

Weaknesses in this category are related to poor coding practices.

SFP Secondary Cluster: Design

This category identifies Software Fault Patterns (SFPs) within the Design cluster.

CERT C++ Secure Coding Section 10 - Environment (ENV)

Weaknesses in this category are related to rules in the Environment (ENV) section of the CERT C++ Secure Coding Standard. Since not all rules map to specific weaknesse...

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses Introduced During Implementation

This view (slice) lists weaknesses that can be introduced during implementation.

Weaknesses in Software Written in Java

This view (slice) covers issues that are found in Java programs that are not common to all languages.

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