C - multiple warnings "pointer is missing a nullability type specifier" when compiling program, what do I do?

Question

I recently started having problems with compiling C programs, getting 10, 20 or 100 warnings from the different C packages like stdio.h or stdlib.h.

The warnings differ somewhat but usually say something like this:

/usr/local/include/_stdio.h:93:16: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or
      _Null_unspecified) [-Wnullability-completeness]
        unsigned char   *_base;

My program still compiles and works fine, but I worry that this needs to be fixed and also it is extremely annoying getting all these warnings in the terminal.

I am almost certain these warnings started showing after I updated my system to macOS Catalina but I don't know where to begin to solve it.

More concretely, when I compile a simple helloworld.c program like so

#include <stdio.h>

int main (void) {
    printf("Hello World!"); 
    return 0; 
}

with the following commands:

make helloworld

or

gcc helloworld.c -o helloworld

..I get the following warnings, even though the program actually compiles.

In file included from helloworld.c:1:
In file included from /usr/local/include/stdio.h:64:
/usr/local/include/_stdio.h:93:16: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Wnullability-completeness]
        unsigned char   *_base;
                        ^
/usr/local/include/_stdio.h:93:16: note: insert '_Nullable' if the pointer may be null
        unsigned char   *_base;
                        ^
                          _Nullable 
/usr/local/include/_stdio.h:93:16: note: insert '_Nonnull' if the pointer should never be null
        unsigned char   *_base;
                        ^
                          _Nonnull 
/usr/local/include/_stdio.h:138:32: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Wnullability-completeness]
        int     (* _Nullable _read) (void *, char *, int);
                                          ^
/usr/local/include/_stdio.h:138:32: note: insert '_Nullable' if the pointer may be null
        int     (* _Nullable _read) (void *, char *, int);
                                          ^
                                           _Nullable
/usr/local/include/_stdio.h:138:32: note: insert '_Nonnull' if the pointer should never be null
        int     (* _Nullable _read) (void *, char *, int);
                                          ^
                                           _Nonnull
/usr/local/include/_stdio.h:138:40: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Wnullability-completeness]
        int     (* _Nullable _read) (void *, char *, int);
                                                  ^
/usr/local/include/_stdio.h:138:40: note: insert '_Nullable' if the pointer may be null
        int     (* _Nullable _read) (void *, char *, int);
                                                  ^
                                                   _Nullable
/usr/local/include/_stdio.h:138:40: note: insert '_Nonnull' if the pointer should never be null
        int     (* _Nullable _read) (void *, char *, int);
                                                  ^
                                                   _Nonnull
/usr/local/include/_stdio.h:139:35: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Wnullability-completeness]
        fpos_t  (* _Nullable _seek) (void *, fpos_t, int);
                                          ^
/usr/local/include/_stdio.h:139:35: note: insert '_Nullable' if the pointer may be null
        fpos_t  (* _Nullable _seek) (void *, fpos_t, int);
                                          ^
                                           _Nullable
/usr/local/include/_stdio.h:139:35: note: insert '_Nonnull' if the pointer should never be null
        fpos_t  (* _Nullable _seek) (void *, fpos_t, int);
                                          ^
                                           _Nonnull
/usr/local/include/_stdio.h:140:32: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Wnullability-completeness]
        int     (* _Nullable _write)(void *, const char *, int);
                                          ^
/usr/local/include/_stdio.h:140:32: note: insert '_Nullable' if the pointer may be null
        int     (* _Nullable _write)(void *, const char *, int);
                                          ^
                                           _Nullable
/usr/local/include/_stdio.h:140:32: note: insert '_Nonnull' if the pointer should never be null
        int     (* _Nullable _write)(void *, const char *, int);
                                          ^
                                           _Nonnull
/usr/local/include/_stdio.h:140:46: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Wnullability-completeness]
        int     (* _Nullable _write)(void *, const char *, int);
                                                        ^
/usr/local/include/_stdio.h:140:46: note: insert '_Nullable' if the pointer may be null
        int     (* _Nullable _write)(void *, const char *, int);
                                                        ^
                                                         _Nullable
/usr/local/include/_stdio.h:140:46: note: insert '_Nonnull' if the pointer should never be null
        int     (* _Nullable _write)(void *, const char *, int);
                                                        ^
                                                         _Nonnull
/usr/local/include/_stdio.h:144:18: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Wnullability-completeness]
        struct __sFILEX *_extra; /* additions to FILE to not break ABI */
                        ^
/usr/local/include/_stdio.h:144:18: note: insert '_Nullable' if the pointer may be null
        struct __sFILEX *_extra; /* additions to FILE to not break ABI */
                        ^
                          _Nullable 
/usr/local/include/_stdio.h:144:18: note: insert '_Nonnull' if the pointer should never be null
        struct __sFILEX *_extra; /* additions to FILE to not break ABI */
                        ^
                          _Nonnull 
In file included from helloworld.c:1:
/usr/local/include/stdio.h:67:13: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Wnullability-completeness]
extern FILE *__stdinp;
            ^
/usr/local/include/stdio.h:67:13: note: insert '_Nullable' if the pointer may be null
extern FILE *__stdinp;
            ^
              _Nullable 
/usr/local/include/stdio.h:67:13: note: insert '_Nonnull' if the pointer should never be null
extern FILE *__stdinp;
            ^
              _Nonnull 
/usr/local/include/stdio.h:386:41: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Wnullability-completeness]
                 int (* _Nullable)(void *, const char *, int),
                                        ^
/usr/local/include/stdio.h:386:41: note: insert '_Nullable' if the pointer may be null
                 int (* _Nullable)(void *, const char *, int),
                                        ^
                                         _Nullable
/usr/local/include/stdio.h:386:41: note: insert '_Nonnull' if the pointer should never be null
                 int (* _Nullable)(void *, const char *, int),
                                        ^
                                         _Nonnull
/usr/local/include/stdio.h:386:55: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Wnullability-completeness]
                 int (* _Nullable)(void *, const char *, int),
                                                      ^
/usr/local/include/stdio.h:386:55: note: insert '_Nullable' if the pointer may be null
                 int (* _Nullable)(void *, const char *, int),
                                                      ^
                                                       _Nullable
/usr/local/include/stdio.h:386:55: note: insert '_Nonnull' if the pointer should never be null
                 int (* _Nullable)(void *, const char *, int),
                                                      ^
                                                       _Nonnull
/usr/local/include/stdio.h:387:44: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Wnullability-completeness]
                 fpos_t (* _Nullable)(void *, fpos_t, int),
                                           ^
/usr/local/include/stdio.h:387:44: note: insert '_Nullable' if the pointer may be null
                 fpos_t (* _Nullable)(void *, fpos_t, int),
                                           ^
                                            _Nullable
/usr/local/include/stdio.h:387:44: note: insert '_Nonnull' if the pointer should never be null
                 fpos_t (* _Nullable)(void *, fpos_t, int),
                                           ^
                                            _Nonnull
/usr/local/include/stdio.h:388:41: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Wnullability-completeness]
                 int (* _Nullable)(void *));
                                        ^
/usr/local/include/stdio.h:388:41: note: insert '_Nullable' if the pointer may be null
                 int (* _Nullable)(void *));
                                        ^
                                         _Nullable
/usr/local/include/stdio.h:388:41: note: insert '_Nonnull' if the pointer should never be null
                 int (* _Nullable)(void *));
                                        ^
                                         _Nonnull
/usr/local/include/stdio.h:384:6: warning: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Wnullability-completeness]
FILE    *funopen(const void *,
        ^
/usr/local/include/stdio.h:384:6: note: insert '_Nullable' if the pointer may be null
FILE    *funopen(const void *,
        ^
          _Nullable 
/usr/local/include/stdio.h:384:6: note: insert '_Nonnull' if the pointer should never be null
FILE    *funopen(const void *,
        ^
          _Nonnull 
13 warnings generated.

EDIT: Mike Minaev provided a temporary fix that I am using for now. Command:

gcc -Wno-nullability-completeness helloworld.c -o helloworld

EDIT: I have looked around and tried various solutions from this thread or this thread, including reinstalling xcode with CLI but without results.

Jonathan Leffler below speculates that it could be because my header files are located in usr/local/includeinstead of usr/include but no fix is suggested.

Comments are not for extended discussion; this conversation has been moved to chat. — Samuel Liew
– Samuel Liew, Commented Oct 17, 2019 at 22:32

Mike Minaev · Accepted Answer · 2019-10-21 14:47:57Z

5

temp quick fix for me:

gcc -Wno-nullability-completeness file.c

answered Oct 21, 2019 at 14:47

Mike Minaev

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3 Comments

bjorkpalm Over a year ago

Thank you! I ran gcc -Wno-nullability-completeness file.c -o file to compile and then ./file to run in my terminal. No warnings appeared, lovely. Question, any specific reason you left out -o file?

Mike Minaev Over a year ago

no, a.out if fine for me. Also if you use pthread library you need to add -Wno-expansion-to-defined

Jonathan Leffler Nov 18 at 19:58

This is still a problem for me in November 2025 with macOS Sequoia 15.6.1 (it annoys me that I can't upgrade my work-controlled machine) with the Tahoe version of XCode 26.1.1 installed. Using cc without any warning options produces a massive onslaught of "nullability completeness" warnings in the system headers. I don't know of workarounds other than adding -Wno-nullability-completeness or using Homebrew's GCC (I'm using gcc-15 (Homebrew GCC 15.2.0) 15.2.0). I've also had issues which needed -Wno-expansion-to-defined and -Wno-nullability-extension on occasion.

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