dont set errno = 0

[rurban]

According to the C Standard (e.g., C99:7.5p3),

"The value of errno is zero at program startup, but is never set to zero by any library function."

$ git grep -n 'errno = 0' src

src/io/fopen_s.c:100:    errno = 0;
src/io/fprintf_s.c:95:    errno = 0;
src/io/freopen_s.c:104:    errno = 0;
src/io/fscanf_s.c:136:    errno = 0;
src/io/gets_s.c:148:    errno = 0;
src/io/scanf_s.c:136:    errno = 0;
src/io/sscanf_s.c:130:    errno = 0;
src/io/tmpfile_s.c:98:    errno = 0;
src/io/vfprintf_s.c:101:    errno = 0;
src/io/vfscanf_s.c:131:    errno = 0;
src/io/vprintf_s.c:87:    errno = 0;
src/io/vscanf_s.c:123:    errno = 0;
src/io/vsscanf_s.c:130:    errno = 0;
src/misc/bsearch_s.c:156:    errno = 0;
src/os/getenv_s.c:142:    errno = 0;
src/os/gmtime_s.c:124:    errno = 0;
src/os/localtime_s.c:126:    errno = 0;
src/str/strtok_s.c:259:    errno = 0;
src/str/vsnprintf_s.c:1186:    errno = 0;
src/str/vsprintf_s.c:115:        errno = 0;
src/wchar/fwprintf_s.c:112:    errno = 0;
src/wchar/fwscanf_s.c:108:        errno = 0;
src/wchar/fwscanf_s.c:137:    errno = 0;
src/wchar/mbsrtowcs_s.c:201:            errno = 0;
src/wchar/mbstowcs_s.c:183:    errno = 0;
src/wchar/mbstowcs_s.c:199:            errno = 0;
src/wchar/snwprintf_s.c:191:    errno = 0;
src/wchar/swprintf_s.c:192:    errno = 0;
src/wchar/swprintf_s.c:202:        errno = 0;
src/wchar/swprintf_s.c:217:            errno = 0; /* EOVERFLOW */
src/wchar/swscanf_s.c:137:    errno = 0;
src/wchar/vfwprintf_s.c:118:    errno = 0;
src/wchar/vfwscanf_s.c:112:        errno = 0;
src/wchar/vfwscanf_s.c:141:    errno = 0;
src/wchar/vsnwprintf_s.c:190:    errno = 0;
src/wchar/vswprintf_s.c:174:    errno = 0;
src/wchar/vswprintf_s.c:198:            errno = 0;
src/wchar/vswscanf_s.c:135:    errno = 0;
src/wchar/vwprintf_s.c:107:    errno = 0;
src/wchar/vwscanf_s.c:128:    errno = 0;
src/wchar/wcstok_s.c:267:    errno = 0;
src/wchar/wscanf_s.c:124:    errno = 0;

From https://www.bugseng.com/blog/c-standard-library-cannot-be-trusted-blindly

[jleffler]

That need not be a problem if each function has the outline: int saved = errno; errno = 0; … if (errno == 0) errno = saved; return …; That is, the function saves the value in errno on entry and restores it before returning if the function (or the functions it calls) have not set errno to a non-zero value.

On Mon, Feb 20, 2023 at 07:02 Reini Urban ***@***.***> wrote: According to the C Standard (e.g., C99:7.5p3), "The value of errno is zero at program startup, but is never set to zero by any library function." git grep 'errno = 0' src src/io/fopen_s.c:100: errno = 0; src/io/fprintf_s.c:95: errno = 0; src/io/freopen_s.c:104: errno = 0; src/io/fscanf_s.c:136: errno = 0; src/io/gets_s.c:148: errno = 0; src/io/scanf_s.c:136: errno = 0; src/io/sscanf_s.c:130: errno = 0; src/io/tmpfile_s.c:98: errno = 0; src/io/vfprintf_s.c:101: errno = 0; src/io/vfscanf_s.c:131: errno = 0; src/io/vprintf_s.c:87: errno = 0; src/io/vscanf_s.c:123: errno = 0; src/io/vsscanf_s.c:130: errno = 0; src/misc/bsearch_s.c:156: errno = 0; src/os/getenv_s.c:142: errno = 0; src/os/gmtime_s.c:124: errno = 0; src/os/localtime_s.c:126: errno = 0; src/str/strtok_s.c:259: errno = 0; src/str/vsnprintf_s.c:1186: errno = 0; src/str/vsprintf_s.c:115: errno = 0; src/wchar/fwprintf_s.c:112: errno = 0; src/wchar/fwscanf_s.c:108: errno = 0; src/wchar/fwscanf_s.c:137: errno = 0; src/wchar/mbsrtowcs_s.c:201: errno = 0; src/wchar/mbstowcs_s.c:183: errno = 0; src/wchar/mbstowcs_s.c:199: errno = 0; src/wchar/snwprintf_s.c:191: errno = 0; src/wchar/swprintf_s.c:192: errno = 0; src/wchar/swprintf_s.c:202: errno = 0; src/wchar/swprintf_s.c:217: errno = 0; /* EOVERFLOW */ src/wchar/swscanf_s.c:137: errno = 0; src/wchar/vfwprintf_s.c:118: errno = 0; src/wchar/vfwscanf_s.c:112: errno = 0; src/wchar/vfwscanf_s.c:141: errno = 0; src/wchar/vsnwprintf_s.c:190: errno = 0; src/wchar/vswprintf_s.c:174: errno = 0; src/wchar/vswprintf_s.c:198: errno = 0; src/wchar/vswscanf_s.c:135: errno = 0; src/wchar/vwprintf_s.c:107: errno = 0; src/wchar/vwscanf_s.c:128: errno = 0; src/wchar/wcstok_s.c:267: errno = 0; src/wchar/wscanf_s.c:124: errno = 0; — Reply to this email directly, view it on GitHub <#129>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACCAHBWF6U5Z5HHFWU7I66TWYN2QTANCNFSM6AAAAAAVB5J6NE> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

-- Jonathan Leffler ***@***.***> #include <disclaimer.h> Guardian of DBD::Informix - v2018.1031 - http://dbi.perl.org "Blessed are we who can laugh at ourselves, for we shall never cease to be amused."

[rurban]

According to the C Standard (e.g., C99:7.5p3),

"The value of errno is zero at program startup, but is never set to zero by any library function."

But this a libc, not just a common library. And the libc mandates to set errno on all cases a syscall fails. And to clear it before each syscall.