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C11 Annex K introduced the new type errno_t that is defined to be type int in errno.h and elsewhere. Many of the functions defined in C11 Annex K return values of this type [ISO/IEC 9899:2011]. The errno_t type should be used as the type of an object that may contain only values that might be found in errno. For example, a function that returns the value of errno should be declared as having the return type errno_t.

This recommendation depends on C11 Annex K being implemented. The following code can be added to remove this dependency:

Code Block

language	cpp

#ifndef __STDC_LIB_EXT1__
  typedef int errno_t;
#endif

Noncompliant Code Example

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This noncompliant code example nevertheless complies with ERR30-C. Set errno to zero before calling a library function known to set errno, and check errno only after the function returns a value indicating failureTake care when reading errno.

Compliant Solution (POSIX)

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This compliant solution is categorized as a POSIX solution because it returns EINVAL and EIO , which are defined by POSIX (IEEE Std 1003.1, 2013 Edition) but not by the C Standard.

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Failing to test for error conditions can lead to vulnerabilities of varying severity. Declaring functions that return an errno with a return type of errno_t will not eliminate this problem but may reduce errors caused by programmers' misunderstanding the purpose of a return value.