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Many existing functions that return errno are declared as returning a value of type int. It is semantically unclear by looking at the function declaration or prototype if these functions return an error status or a value or, worse, some combination of the two. (See ERR02-C. Avoid in-band error indicators.)
TR 24731-1 introduced 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 TR 24731-1 C11 Annex K return values of this type [TR 24731-1ISO/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 TR 24731-1 C11 Annex K being implemented and advocates using errno_t in new code where appropriate.
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#include <errno.h>
#include <stdio.h>
enum { NO_FILE_POS_VALUES = 3 };
int opener(
FILE *file,
int *width,
int *height,
int *data_offset
) {
int file_w;
int file_h;
int file_o;
fpos_t offset;
if (file == NULL) { return EINVAL; }
errno = 0;
if (fgetpos(file, &offset) != 0) { return errno; }
if (fscanf(file, "%i %i %i", &file_w, &file_h, &file_o)
!= NO_FILE_POS_VALUES) {
return EIO;
}
errno = 0;
if (fsetpos(file, &offset) != 0) { return errno; }
if (width != NULL) { *width = file_w; }
if (height != NULL) { *height = file_h; }
if (data_offset != NULL) { *data_offset = file_o; }
return 0;
}
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#include <errno.h>
#include <stdio.h>
enum { NO_FILE_POS_VALUES = 3 };
errno_t opener(
FILE *file,
int *width,
int *height,
int *data_offset
) {
int file_w;
int file_h;
int file_o;
fpos_t offset;
if (file == NULL) { return EINVAL; }
errno = 0;
if (fgetpos(file, &offset) != 0 ) { return errno; }
if (fscanf(file, "%i %i %i", &file_w, &file_h, &file_o)
!= NO_FILE_POS_VALUES) {
return EIO;
}
errno = 0;
if (fsetpos(file, &offset) != 0 ) { return errno; }
if (width != NULL) { *width = file_w; }
if (height != NULL) { *height = file_h; }
if (data_offset != NULL) { *data_offset = file_o; }
return 0;
}
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| CERT C++ Secure Coding Standard | DCL09-CPP. Declare functions that return errno with a return type of errno_t |
| ISO/IEC TR 24731-1:20079899:2011 | K.3.2 Errors <errno.h> |
| ISO/IEC TR 24772:2013 | Ignored Error Status and Unhandled Exceptions [OYB] |
| MISRA C:2012 | Directive 1.1 (required) |
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