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No other identifiers are reserved. (The POSIX standard extends the set of identifiers reserved by the C Standard to include an open-ended set of its own. See Portable Operating System Interface [POSIX^®], Base Specifications, Issue 7, Section 2.2, "The Compilation Environment" [IEEE Std 1003.1-2013].) The behavior of a program that declares or defines an identifier in a context in which it is reserved or that defines a reserved identifier as a macro name is undefined. (See undefined behavior 106.)

Noncompliant Code Example (

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Include Guard)

A common, but noncompliant, practice is to choose a reserved name for a macro used in a preprocessor conditional guarding against multiple inclusions of a header file. (See also PRE06-C. Enclose header files in an inclusion include guard.) The name may clash with reserved names defined by the implementation of the C standard library in its headers or with reserved names implicitly predefined by the compiler even when no C standard library header is included.

#ifndef _MY_HEADER_H_
#define _MY_HEADER_H_

/* Contents of <my_header.h> */

#endif /* _MY_HEADER_H_ */

Compliant Solution (

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Include Guard)

This compliant solution avoids using leading underscores in the macro name of the header include guard:

#ifndef MY_HEADER_H
#define MY_HEADER_H

/* Contents of <my_header.h> */

#endif /* MY_HEADER_H */

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Using reserved identifiers can lead to incorrect program operation.

Automated Detection

Related Guidelines

Bibliography

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