Question

我对C中的函数宏定义有疑问（我是初学者）：我有一个使用lib.a函数的COTS库strtok()，但是我的CERT应用程序仅支持strtok_r，所以在编译时会出错。

如何在头文件中定义strtok函数，以strtok_r覆盖？

我尝试过类似的操作，但出现错误：

extern char *strtok_r(char *s1, const char *s2, char **saveptr);
#define strtok(s1,s2) strtok_r(s1,s2,saveptr)

哪种方法是达到结果的最佳而干净的方法？

非常感谢您的投入。

Answer 1

假设我正确理解了你

您没有strtok功能。
您使用内部使用libother.a-函数的库strtok（只是为其命名）。
您没有该库的源代码。

Rob步入正轨，但我认为绕错了方向...

您可以通过包装strtok函数来构建自己的strtok_r函数：

将此功能插入您的源文件之一：

char *strtok(char *s1, const char *delim) {
    static char* saveptr = 0;
    return strtok_r(s1, delim, &saveptr);
}

然后以常规方式编译和链接代码

gcc your_code_file.c -lother -o your_binary

应该做。但是：有一个理由说明为什么您更喜欢使用strtok_r而不是strtok： strtok一次只能解析一个字符串，strtok_r允许同时解析任意数量的不同字符串。

有了上面的“ hack”，您就失去了strtok_r的优势。

Answer 2

您不能将strtok_r重新定义为strtok，因为它们与不同数量的参数一起以不同的方式运行。

char * strtok（char * restrict，const char * restrict）;

char * strtok_r（char *，const char *，char **）;

如果您没有strtok_r，那么写一个就可以了。

评论员解释说，您希望从strtok_r实现strtok，所以我也包括了该代码。

这是来自WoBoq的strtok_r（）

/* Reentrant string tokenizer.  Generic version.
   Copyright (C) 1991-2018 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <string.h>

#ifndef _LIBC
/* Get specification.  */
# include "strtok_r.h"
# define __strtok_r strtok_r
#endif

/* Parse S into tokens separated by characters in DELIM.
   If S is NULL, the saved pointer in SAVE_PTR is used as
   the next starting point.  For example:
        char s[] = "-abc-=-def";
        char *sp;
        x = strtok_r(s, "-", &sp);        // x = "abc", sp = "=-def"
        x = strtok_r(NULL, "-=", &sp);        // x = "def", sp = NULL
        x = strtok_r(NULL, "=", &sp);        // x = NULL
                // s = "abc\0-def\0"
*/

char *
__strtok_r (char *s, const char *delim, char **save_ptr)
{
  char *end;

  if (s == NULL)
    s = *save_ptr;

  if (*s == '\0')
    {
      *save_ptr = s;
      return NULL;
    }

  /* Scan leading delimiters.  */
  s += strspn (s, delim);
  if (*s == '\0')
    {
      *save_ptr = s;
      return NULL;
    }

  /* Find the end of the token.  */
  end = s + strcspn (s, delim);
  if (*end == '\0')
    {
      *save_ptr = end;
      return s;
    }

  /* Terminate the token and make *SAVE_PTR point past it.  */
  *end = '\0';
  *save_ptr = end + 1;
  return s;
}
#ifdef weak_alias
libc_hidden_def (__strtok_r)
weak_alias (__strtok_r, strtok_r)
#endif

这是来自glibc/blob/master/string/strtok.c的strtok（）

/* Copyright (C) 1991-2018 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.
   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <string.h>

/* Parse S into tokens separated by characters in DELIM.
   If S is NULL, the last string strtok() was called with is
   used.  For example:
    char s[] = "-abc-=-def";
    x = strtok(s, "-");     // x = "abc"
    x = strtok(NULL, "-=");     // x = "def"
    x = strtok(NULL, "=");      // x = NULL
        // s = "abc\0=-def\0"
*/
char *
strtok (char *s, const char *delim)
{
  static char *olds;
  return __strtok_r (s, delim, &olds);
}

这是每个函数的一个示例实现。有很多包含该库的编译器源。如果该许可证不符合您的要求，请尝试搜索另一个满足您要求的条款或编写您自己的功能。

只需将该源代码写入一个单独的文件，然后将其添加到您的链接列表中即可。

在此GeeksForGeeks网页“ strtok() and strtok_r() functions in C with examples”中解释并演示了尝试重新定义这些功能的问题。与第一次调用所提供的参数相比，strtok_r函数对后续调用的参数要求不同。用可以决定是要设置还是要测试的全局变量进行定义并不方便。

C在头文件中定义指向外部函数的宏函数

2 个答案: