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Noncompliant Code Example (Identifiers with External Linkage)
In addition to symbols defined as functions in each C standard library header, identifiers with external linkage include errno and math_errhandling, among others, regardless of whether any of them are masked by a macro of the same name.
This noncompliant example provides definitions for the C standard library functions malloc() and free(). Although this practice is permitted by many traditional implementations of UNIX (for example, the Dmalloc library), it is undefined behavior according to the C Standard. Even on systems that allow replacing malloc(), doing so without also replacing aligned_alloc(), calloc(), and realloc() is likely to cause problems.
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Noncompliant Code Example (errno)
In addition to symbols defined as functions in each C standard library header, identifiers with external linkage include errno and math_errhandling, among others, regardless of whether any of them are masked by a macro of the same name.
According to the C Standard, 7.5, paragraph 2 [ISO/IEC 9899:2011], the behavior of a program is undefined when
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