C 在头文件中定义一个指向外部函数的宏函数
C define a macro function in header file pointing to an extern function
我对C
中的函数宏定义有疑问(我是初学者):
我有一个使用 strtok()
函数的 COTS 库 lib.a
,但我的 CERT 应用程序只支持 strtok_r
,所以我在编译时遇到错误。
我如何在头文件中定义 strtok
函数应该被 strtok_r
覆盖?
我试过类似的方法,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)
哪种方法是实现结果的最佳且简洁的方法?
非常感谢您的意见。
您不能将 strtok_r 重新定义为 strtok,因为随着参数数量的不同,它们的操作也不同。
char *strtok(char *restrict, const char *restrict);
char *strtok_r(char *, const char *, char **);
如果你没有 strtok_r 那么写一个是最好的方法。
一位评论员解释说您希望从 strtok_r 实现 strtok,所以我也包括了它的代码。
这是 strtok_r() 来自:WoBoq
/* 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[=10=]-def[=10=]"
*/
char *
__strtok_r (char *s, const char *delim, char **save_ptr)
{
char *end;
if (s == NULL)
s = *save_ptr;
if (*s == '[=10=]')
{
*save_ptr = s;
return NULL;
}
/* Scan leading delimiters. */
s += strspn (s, delim);
if (*s == '[=10=]')
{
*save_ptr = s;
return NULL;
}
/* Find the end of the token. */
end = s + strcspn (s, delim);
if (*end == '[=10=]')
{
*save_ptr = end;
return s;
}
/* Terminate the token and make *SAVE_PTR point past it. */
*end = '[=10=]';
*save_ptr = end + 1;
return s;
}
#ifdef weak_alias
libc_hidden_def (__strtok_r)
weak_alias (__strtok_r, strtok_r)
#endif
这是 strtok() 来自:glibc/blob/master/string/strtok.c
/* 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[=11=]=-def[=11=]"
*/
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。有许多包含该库的编译器源可用。如果该许可证不符合您的要求,请尝试搜索另一个符合您需要的条款或编写您自己的函数。
只需将该源写入一个单独的文件并将其添加到您的 link 列表中。
在这个 GeeksForGeeks 网页“strtok() and strtok_r() functions in C with examples”上解释和演示了尝试重新定义这些函数的问题。 strtok_r 函数需要为后续调用提供的参数不同于为第一次调用提供的参数。不方便做一个define,用一个全局的,可以决定是设置还是测试。
假设我理解正确:
- 您没有可用的
strtok
功能。
- 您使用的库
libother.a
(只是给它起个名字)在内部使用 strtok
- 函数。
- 您没有这个库的源代码。
Rob 走在正确的轨道上,但我认为走错了路...
您可以像这样包装 strtok_r
函数来构建自己的 strtok
函数:
将此函数插入您的 源文件之一:
char *strtok(char *s1, const char *delim) {
static char* saveptr = 0;
return strtok_r(s1, delim, &saveptr);
}
然后像
这样的通常方式编译和链接你的代码
gcc your_code_file.c -lother -o your_binary
应该做的。
但是:有一个理由说明为什么您应该更喜欢使用 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。
上面的 'hack' 你失去了 strtok_r
的优势。
我对C
中的函数宏定义有疑问(我是初学者):
我有一个使用 strtok()
函数的 COTS 库 lib.a
,但我的 CERT 应用程序只支持 strtok_r
,所以我在编译时遇到错误。
我如何在头文件中定义 strtok
函数应该被 strtok_r
覆盖?
我试过类似的方法,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)
哪种方法是实现结果的最佳且简洁的方法?
非常感谢您的意见。
您不能将 strtok_r 重新定义为 strtok,因为随着参数数量的不同,它们的操作也不同。
char *strtok(char *restrict, const char *restrict);
char *strtok_r(char *, const char *, char **);
如果你没有 strtok_r 那么写一个是最好的方法。
一位评论员解释说您希望从 strtok_r 实现 strtok,所以我也包括了它的代码。
这是 strtok_r() 来自:WoBoq
/* 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[=10=]-def[=10=]"
*/
char *
__strtok_r (char *s, const char *delim, char **save_ptr)
{
char *end;
if (s == NULL)
s = *save_ptr;
if (*s == '[=10=]')
{
*save_ptr = s;
return NULL;
}
/* Scan leading delimiters. */
s += strspn (s, delim);
if (*s == '[=10=]')
{
*save_ptr = s;
return NULL;
}
/* Find the end of the token. */
end = s + strcspn (s, delim);
if (*end == '[=10=]')
{
*save_ptr = end;
return s;
}
/* Terminate the token and make *SAVE_PTR point past it. */
*end = '[=10=]';
*save_ptr = end + 1;
return s;
}
#ifdef weak_alias
libc_hidden_def (__strtok_r)
weak_alias (__strtok_r, strtok_r)
#endif
这是 strtok() 来自:glibc/blob/master/string/strtok.c
/* 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[=11=]=-def[=11=]"
*/
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。有许多包含该库的编译器源可用。如果该许可证不符合您的要求,请尝试搜索另一个符合您需要的条款或编写您自己的函数。
只需将该源写入一个单独的文件并将其添加到您的 link 列表中。
在这个 GeeksForGeeks 网页“strtok() and strtok_r() functions in C with examples”上解释和演示了尝试重新定义这些函数的问题。 strtok_r 函数需要为后续调用提供的参数不同于为第一次调用提供的参数。不方便做一个define,用一个全局的,可以决定是设置还是测试。
假设我理解正确:
- 您没有可用的
strtok
功能。 - 您使用的库
libother.a
(只是给它起个名字)在内部使用strtok
- 函数。 - 您没有这个库的源代码。
Rob 走在正确的轨道上,但我认为走错了路...
您可以像这样包装 strtok_r
函数来构建自己的 strtok
函数:
将此函数插入您的 源文件之一:
char *strtok(char *s1, const char *delim) {
static char* saveptr = 0;
return strtok_r(s1, delim, &saveptr);
}
然后像
这样的通常方式编译和链接你的代码gcc your_code_file.c -lother -o your_binary
应该做的。
但是:有一个理由说明为什么您应该更喜欢使用 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。
上面的 'hack' 你失去了 strtok_r
的优势。