我最近开始在编译C程序时遇到问题，从不同的C包（如stdio.h或stdlib.h）获得10、20或100条警告。
警告有些不同，但通常会这样说：
/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;
我的程序仍然可以编译并且可以正常运行，但是我担心此问题必须解决，并且在终端中收到所有这些警告也非常烦人。
我几乎可以肯定，在将系统更新为macOS Catalina之后，这些警告开始显示，但是我不知道从哪里开始解决它。
更具体地说，当我像这样编译一个简单的helloworld.c程序时
#include <stdio.h>
int main (void) {
printf("Hello World!");
return 0;
}
使用以下命令：
make helloworld
或
gcc helloworld.c -o helloworld
..即使程序实际上已编译，我仍收到以下警告。
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.
编辑：Mike Minaev提供了我现在正在使用的临时修复程序。命令：
gcc -Wno-nullability-completeness helloworld.c -o helloworld
编辑：我环顾四周并尝试了this thread或this thread的各种解决方案，包括使用CLI重新安装xcode，甚至尝试将以下代码添加到stdio.h（但现在将其删除）：
NS_ASSUME_NONNULL_BEGIN
NS_ASSUME_NONNULL_END
..但没有结果。
Jonathan Leffler下面推测这可能是因为我的头文件位于usr/local/include中而不是usr/include中，但未建议修复。
为我快速修复：
gcc -Wno-nullability-completeness file.c