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The following definition for static_assert() from recommendation DCL03-C. Use a static assertion to test the value of a constant expression uses the JOIN() macro to concatenate the token assertion_failed_at_line_ with the value of __LINE__.

#define static_assert(e) \
  typedef char JOIN(assertion_failed_at_line_, __LINE__) \
    [(e) ? 1 : -1]

__LINE__ is a predefined macro names which expands to an integer constant representing the presumed line number of the current source line within the current source file [ISO/IEC 9899:19992011].

If the intention is to expand the __LINE__ macro, which is likely the case here, the following definition for JOIN() is noncompliant:

#define JOIN(x, y) x ## y

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#define JOIN(x, y) JOIN_AGAIN(x, y)
#define JOIN_AGAIN(x, y) x ## y

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Note also that macro parameters cannot be individually parenthesized when concatenating tokens using the ## operator, converting macro parameters to strings using the # operator, or concatenating adjacent string literals. This is an exception, PRE01-EX2, to recommendation PRE01-C. Use parentheses within macros around parameter names.

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#define str(s) #s
#define foo 4

str(foo)

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#define xstr(s) str(s)
#define str(s) #s
#define foo 4

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Automated Detection

Related Vulnerabilities

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

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CERT C++ Secure Coding Standard: PRE05-CPP. Understand macro replacement when concatenating tokens or performing stringification

ISO/IEC 9899:19992011 Section 6.10.3, "Macro replacement," Section 6.10.3.32, "The ## # operator," Section 6.10.3.23, "The # ## operator," Section 6.10.3.4, "Rescanning and further replacement," and Section 6.10.8, "Predefined macro names"

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[FSF 2005] Section 3.4, "Stringification" and Section 3.5, "Concatenation"
[Saks 2008]

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