Stack Overflow user "pmor" has put together a C source file that demonstrates a large number of similar problems, identifiers that should not be visible in a strictly conforming compiler but are visible with "gcc -std=c11 -pedantic".
A few of the symbols, namely gmtime_r, localtime_r, and timegm, are declared in <time.h> in C23, but not in earlier editions of the C standard. They should not be visible unless you use "-std=c23" or "-std=gnu23" (the latter is the default in more recent versions of gcc. The program is here: https://godbolt.org/z/Pr1obzYxx And just in case that link isn't permanent, here's the code: #include <assert.h> #include <iso646.h> #include <stdarg.h> #include <string.h> #include <complex.h> #include <limits.h> #if __STDC_NO_ATOMICS__ != 1 #include <stdatomic.h> #endif #include <tgmath.h> #include <ctype.h> #include <locale.h> #include <stdbool.h> #include <time.h> #include <errno.h> #include <math.h> #include <stddef.h> #include <uchar.h> #include <fenv.h> #include <setjmp.h> #include <stdint.h> #include <wchar.h> #include <float.h> #include <signal.h> #include <stdio.h> #include <wctype.h> #include <inttypes.h> #include <stdalign.h> #include <stdlib.h> typedef struct { int x; } T; T BUS_ADRALN; T BUS_ADRERR; T BUS_OBJERR; T CLD_CONTINUED; T CLD_DUMPED; T CLD_EXITED; T CLD_KILLED; T CLD_STOPPED; T CLD_TRAPPED; T FPE_FLTDIV; T FPE_FLTINV; T FPE_FLTOVF; T FPE_FLTRES; T FPE_FLTSUB; T FPE_FLTUND; T FPE_INTDIV; T FPE_INTOVF; T ILL_BADSTK; T ILL_COPROC; T ILL_ILLADR; T ILL_ILLOPC; T ILL_ILLOPN; T ILL_ILLTRP; T ILL_PRVOPC; T ILL_PRVREG; T SEGV_ACCERR; T SEGV_MAPERR; T SIGEV_NONE; T SIGEV_SIGNAL; T SIGEV_THREAD; T SI_ASYNCIO; T SI_KERNEL; T SI_MESGQ; T SI_QUEUE; T SI_TIMER; T SI_USER; T addr_t; T asctime_r; T blkcnt_t; T blksize_t; T caddr_t; T clock_getcpuclockid; T clock_getenable_attr; T clock_getres; T clock_gettime; T clock_nanosleep; T clock_setenable_attr; T clock_setres; T clock_settime; T clockid_t; T cpu_set_t; T ctime_r; T daddr_t; T dev_t; T error_t; struct flock { int x; }; T fpurge; T fsblkcnt_t; T fsfilcnt_t; T gammaf; T getdelim; T getline; T getprogname; T gid_t; T gmtime_r; T gnu_dev_major; T gnu_dev_makedev; T gnu_dev_minor; T id_t; T infinity; T infinityf; T ino_t; struct itimerspec { int x; }; T key_t; T localtime_r; T loff_t; T memalign; T mkdtemp; T mode_t; T nanosleep; T nlink_t; T off_t; T pid_t; T program_invocation_name; T program_invocation_short_name; T psignal; T pthread_attr_t; T pthread_barrier_t; T pthread_barrierattr_t; T pthread_cond_t; T pthread_condattr_t; T pthread_key_t; T pthread_mutex_t; T pthread_mutexattr_t; T pthread_once_t; T pthread_rwlock_t; T pthread_rwlockattr_t; T pthread_spinlock_t; T pthread_t; T register_t; T sbintime_t; T setprogname; struct sigaltstack { int x; }; struct sigevent { int x; }; T sigevent_t; T sigset_t; struct sigval { int x; }; T sigval_t; T stack_t; T strtosigno; T suseconds_t; T sys_errlist; T sys_nerr; T timegm; T timelocal; T timer_create; T timer_delete; T timer_getoverrun; T timer_gettime; T timer_settime; T timer_t; T timespec_t; T timestruc_t; T u_int16_t; T u_int32_t; T u_int64_t; T u_int8_t; T uid_t; T useconds_t; T vm_object_t; T vm_offset_t; T vm_size_t; T wcslcat; T wcslcpy; int main(void) { } On Thu, Oct 23, 2025 at 8:28 PM Keith Thompson <[email protected]> wrote: > > The "getline" function is specified by POSIX to be declared > in <stdio.h>. It is not specified by the ISO C standard, so the > identifier should be available for use in strictly conforming > programs. > > $ cat getline_bug.c > #include <stdio.h> > int getline = 0; > int main(void) { > return getline; > } > $ gcc --version > gcc (GCC) 16.0.0 20250907 (experimental) > Copyright (C) 2025 Free Software Foundation, Inc. > This is free software; see the source for copying conditions. There is NO > warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. > > $ gcc getline_bug.c -o getline_bug > getline_bug.c:2:5: error: ‘getline’ redeclared as different kind of symbol > 2 | int getline = 0; > | ^~~~~~~ > In file included from /usr/include/stdio.h:85, > from getline_bug.c:1: > /usr/include/sys/stdio.h:35:9: note: previous declaration of ‘getline’ with > type ‘ssize_t(char **, size_t *, FILE *)’ {aka ‘long int(char **, long > unsigned int *, FILE *)’} > 35 | ssize_t getline (char **, size_t *, FILE *); > | ^~~~~~~ > > $ > > Stack Overflow user "pmor" reports the same problem with gcc 12.4.0. > > The problem is in newlib, winsup/cygwin/include/sys/stdio.h, line 35. > I expect getdelim() to exhibit the same problem, but I haven't checked that. > > GNU libc's <stdio.h> avoids this problem by surrounding the > declarations of getline() and getdelim() by an appropriate #ifdef. -- Problem reports: https://cygwin.com/problems.html FAQ: https://cygwin.com/faq/ Documentation: https://cygwin.com/docs.html Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple
