史崔托克的错误我这里漏了点东西

这是我的程序的一个片段

#include <stdio.h>
#include <string.h>
void  something_wrong_really(char *str)
{
        char *savedptr = NULL;
        char *delim    = " ";

        for ( char *p = str ; ; p = NULL) {
                char *token = strtok_r(p, delim, &savedptr);
                if (token == NULL)
                        break;
                printf(" %s\n", token);
        }
}

int main(void) {
    char str[] = "Okay so lets split this and see how it works";
    something_wrong_really(str);
    return 0;
}

strtok_r manual

strtok_r():_POSIX_C_源 /|BSD|u源| | SVID|u源

如果我把程序编译成

cc t.c -std=c99

t.c: In function 'something_wrong_really':
t.c:10:3: warning: implicit declaration of function 'strtok_r' [-Wimplicit-function-declaration]
   char *token = strtok_r(p, delim, &savedptr);
   ^
t.c:10:17: warning: initialization makes pointer from integer without a cast [enabled by default]
   char *token = strtok_r(p, delim, &savedptr);
                 ^

有什么比这更糟的吗 segfaults

./a.out
Segmentation fault

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7a5af19 in vfprintf () from /lib64/libc.so.6
Missing separate debuginfos, use: debuginfo-install glibc-2.17-222.el7.x86_64
(gdb) bt
#0  0x00007ffff7a5af19 in vfprintf () from /lib64/libc.so.6
#1  0x00007ffff7a61339 in printf () from /lib64/libc.so.6
#2  0x00000000004005e2 in something_wrong_really (str=0x7fffffffe0a0 "Okay") at t.c:13
#3  0x0000000000400653 in main () at t.c:19
(gdb)

 _SVID_SOURCE || _BSD_SOURCE || _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE

相应的输出

# cc t.c -std=c99 -D_BSD_SOURCE
#
#
# ./a.out
 Okay
 so
 lets
 split
 this
 and
 see
 how
 it
 works
#

关于为什么会有这种行为有什么线索吗?

所以这似乎是 strtok_r

glibc的特性测试宏要求(参见 功能测试宏(7):

   strtok_r(): _POSIX_C_SOURCE
       || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

feature_test_macros

,必须进行以下宏定义之一 在包含任何头文件之前:

       #define _BSD_SOURCE
       #define _XOPEN_SOURCE        /* or any value < 500 */

   Alternatively, equivalent definitions can be included in the compila‐
   tion command:

       cc -D_BSD_SOURCE
       cc -D_XOPEN_SOURCE           # Or any value < 500

因此,正如@someprogrammer dude指出的,包含这些宏定义是必须的,否则它将导致UB,这最终就是这里发生的事情。