Lowercase letter l (ell) can easily be confused with the digit 1 (one). This can be particularly confusing when indicating that an integer literal constant is a long value. This recommendation is similar to DCL02-C. Use visually distinct identifiers. Likewise, you should use uppercase LL rather than lowercase ll when indicating that an integer literal constant is a long long value.

To be precise when using modifiers to indicate the type of an integer literal, the first character may not be l.  It may be L, u, or U. Subsequent characters have no strict case requirements.

Noncompliant Code Example

This noncompliant example highlights the result of adding an integer and a long value even though it appears that two integers 1111 are being added:

	printf("Sum is %ld\n", 1111 + 111l);

Compliant Solution

The compliant solution improvises by using an uppercase L instead of lowercase l to disambiguate the visual appearance:

	printf("Sum is %ld\n", 1111 + 111L);

Risk Assessment

Confusing a lowercase letter l (ell) with a digit 1 (one) when indicating that an integer denotation is a long value could lead to an incorrect value being written into code.

Automated Detection

Tool	Version	Checker	Description
Astrée		long-suffix	Fully checked
Axivion Bauhaus Suite		CertC-DCL16
CodeSonar		LANG.TYPE.CSUF	Confusing literal suffix
ECLAIR		CC2.DCL16	Fully implemented
Helix QAC		C1280
LDRA tool suite		252 S	Fully implemented
Parasoft C/C++test		CERT_C-DCL16-a	The lowercase form of 'L' shall not be used as the first character in a literal suffix
PC-lint Plus		620	Fully supported
Polyspace Bug Finder		CERT C: Rec. DCL16-C	Checks for use of lowercase "l" in literal suffix (rec. fully covered)
RuleChecker		long-suffix	Fully checked
SonarQube C/C++ Plugin		LiteralSuffix

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Related Guidelines

Bibliography