CERT C: Rec. DCL02-C

Use visually distinct identifiers

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Description

Rule Definition

Use visually distinct identifiers.¹

Polyspace Implementation

The rule checker checks for Use of typographically ambiguous identifiers.

Examples

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Use of typographically ambiguous identifiers

Issue

The issue occurs when you use identifiers in the same name space with overlapping visibility and the identifiers are not typographically unambiguous.

Risk

What “unambiguous” means depends on the alphabet and language in which source code is written. When you use identifiers that are typographically close, you can confuse between them.

For the Latin alphabet as used in English words, at a minimum, the identifiers should not differ by:

The interchange of a lowercase letter with its uppercase equivalent.
The presence or absence of the underscore character.
The interchange of the letter O and the digit 0.
The interchange of the letter I and the digit 1.
The interchange of the letter I and the letter l.
The interchange of the letter S and the digit 5.
The interchange of the letter Z and the digit 2.
The interchange of the letter n and the letter h.
The interchange of the letter B and the digit 8.
The interchange of the letters rn and the letter m.

Example - Typographically Ambiguous Identifiers

void func(void) {
    int id1_numval;
    int id1_num_val;  /* Non-compliant */

    int id2_numval;
    int id2_numVal;   /* Non-compliant */

    int id3_lvalue;
    int id3_Ivalue;   /* Non-compliant */

    int id4_xyZ;
    int id4_xy2;      /* Non-compliant */

    int id5_zerO;
    int id5_zer0;     /* Non-compliant */

    int id6_rn;
    int id6_m;        /* Non-compliant */
}

In this example, the rule is violated when identifiers that can be confused for each other are used.

Check Information

Group: Rec. 02. Declarations and Initialization (DCL)

Version History

Introduced in R2019a

¹ This software has been created by MathWorks incorporating portions of: the “SEI CERT-C Website,” © 2017 Carnegie Mellon University, the SEI CERT-C++ Web site © 2017 Carnegie Mellon University, ”SEI CERT C Coding Standard – Rules for Developing safe, Reliable and Secure systems – 2016 Edition,” © 2016 Carnegie Mellon University, and “SEI CERT C++ Coding Standard – Rules for Developing safe, Reliable and Secure systems in C++ – 2016 Edition” © 2016 Carnegie Mellon University, with special permission from its Software Engineering Institute.

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