MISRA.STDLIB.ERRNO

Use of error indicator 'errno'.

MISRA-C Rule 20.5 (required): The error indicator errno shall not be used.

This rule is also covered byMISRA.EXPANSION.UNSAFE

[Implementation 46, Koenig 73]

errno is a facility of C, which in theory should be useful, but which in practice is poorly defined by the standard. A non zero value may or may not indicate that a problem has occurred; as a result it shall not be used. Even for those functions for which the behaviour of errno is well defined, it is preferable to check the values of inputs before calling the function rather than rely on using errno to trap errors (see Rule 16.10).

MISRA-C++ Rule 19-3-1 (required): The error indicator errno shall not be used.

This rule is also covered by MISRA.EXPANSION.UNSAFE.

Rationale

errno is a facility of C++ which should in theory be useful, but which in practice is poorly defined by ISO/IEC 14882:2003 [1]. A non-zero value may or may not indicate that a problem has occurred; therefore errno shall not be used.

Even for those functions for which the behaviour of errno is well defined, it is preferable to check the values of inputs before calling the function rather than relying on using errno to trap errors.

Example

#include <cstdlib>
#include <cerrno>

void f1 ( const char_t * str )
{
   errno = 0;        // Non-compliant
   int32_t i = atoi ( str );
   if ( 0 != errno ) // Non-compliant
   {
      // handle error case???
   }
}