C wrapper to errno

Question

I've written the function to wrap an errno, but I have compile error: error: ‘EACCES’ undeclared (first use in this function) case EACCES: What I'm doing wrong? How can I wrap the errno with switch-case? status_t defined as enum of relevant errors.

static status_t GetErrorStatus (int errno_value) { status_t err_status = COMMON_ERROR; switch (errno_value) { case EACCES: err_status = NO_ACCESS_PERMISSION; break; case EPERM: err_status = NO_ACCESS_PERMISSION; break; case EIDRM: err_status = SEMAPHORE_REMOVED; break; case ENOENT: err_status = FILE_DOESNT_EXIST; break; case EEXIST: err_status = SEMAPHORE_ALREADY_EXISTS; break; default: err_status = COMMON_ERROR; } return (err_status); }

Why copy errno values to what looks like an enum or another set of macros representing integral values? — Govind Parmar
– Govind Parmar, Commented Dec 4, 2018 at 19:50
@GovindParmar I can think of 2 useful reason: grouping of errors as done above with EACCES, EPERM into NO_ACCESS_PERMISSION and allowing a desired sequent index or bit mask of error identifiers. — chux
– chux, Commented Dec 4, 2018 at 20:04

chux · Accepted Answer · 2018-12-04 20:06:06Z

How can I wrap the errno with switch-case?

Not all platforms support the various errors. C specifies only 3: EDOM EILSEQ ERANGE in <errno.h> and, importantly, they are macros. I'd expect additional platform specific errors to also be so testable.

 switch (errno_value) { #ifdef EACCES case EACCES: err_status = NO_ACCESS_PERMISSION; break; #endif #ifdef EPERM case EPERM: err_status = NO_ACCESS_PERMISSION; break; #endif ...

Basile Starynkevitch · Accepted Answer · 2018-12-04 19:49:02Z

Show a complete code.

My guess is that you forgot to #include <errno.h> or that on your particular system EACCESS is not defined.

On Linux, read errno(3). EACCESS is mentioned as POSIX, so on some non-POSIX systems it might not be defined.

The C11 standard n1570 mentions errno in its §7.5 and EACCESS is not listed there. If it exists, it should be a macro, so you might wrap some appropriate part of your code with #ifdef EACCESS ... #endif

"you forgot to #include <errno.h>" - You are absolutely right!!! I've added it and now compiler is quiet. Thanks!

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