[英]How portable is the re-entrant qsort_r function compared to qsort?
qsort_r()
is the re-entrant version of qsort()
which takes an additional 'thunk' argument and passes it into the compare function and I'd like to be able to use it in portable C code. qsort_r()
是qsort()
可重入版本,它接受一个额外的'thunk'参数并将其传递给compare函数,我希望能够在便携式C代码中使用它。 qsort()
is POSIX and everywhere but qsort_r()
seems to be a BSD extension. qsort()
是POSIX和无处不在,但qsort_r()
似乎是一个BSD扩展。 As a specific question, does this exist or have an equivalent in the Windows C runtime? 作为一个特定问题,这是否存在或在Windows C运行时具有等效?
I've attempted to write a portable version of qsort_r / qsort_s (called sort_r) shown with an example. 我试图用一个例子来编写一个可移植版本的qsort_r / qsort_s(称为sort_r)。 I've also put this code in a git repo ( https://github.com/noporpoise/sort_r )
我也把这个代码放在git repo中( https://github.com/noporpoise/sort_r )
struct sort_r_data
{
void *arg;
int (*compar)(const void *a1, const void *a2, void *aarg);
};
int sort_r_arg_swap(void *s, const void *aa, const void *bb)
{
struct sort_r_data *ss = (struct sort_r_data*)s;
return (ss->compar)(aa, bb, ss->arg);
}
void sort_r(void *base, size_t nel, size_t width,
int (*compar)(const void *a1, const void *a2, void *aarg), void *arg)
{
#if (defined _GNU_SOURCE || defined __GNU__ || defined __linux__)
qsort_r(base, nel, width, compar, arg);
#elif (defined __APPLE__ || defined __MACH__ || defined __DARWIN__ || \
defined __FREEBSD__ || defined __BSD__ || \
defined OpenBSD3_1 || defined OpenBSD3_9)
struct sort_r_data tmp;
tmp.arg = arg;
tmp.compar = compar;
qsort_r(base, nel, width, &tmp, &sort_r_arg_swap);
#elif (defined _WIN32 || defined _WIN64 || defined __WINDOWS__)
struct sort_r_data tmp = {arg, compar};
qsort_s(*base, nel, width, &sort_r_arg_swap, &tmp);
#else
#error Cannot detect operating system
#endif
}
Example usage: 用法示例:
#include <stdio.h>
/* comparison function to sort an array of int, inverting a given region
`arg` should be of type int[2], with the elements
representing the start and end of the region to invert (inclusive) */
int sort_r_cmp(const void *aa, const void *bb, void *arg)
{
const int *a = aa, *b = bb, *p = arg;
int cmp = *a - *b;
int inv_start = p[0], inv_end = p[1];
char norm = (*a < inv_start || *a > inv_end || *b < inv_start || *b > inv_end);
return norm ? cmp : -cmp;
}
int main()
{
/* sort 1..19, 30..20, 30..100 */
int arr[18] = {1, 5, 28, 4, 3, 2, 10, 20, 18, 25, 21, 29, 34, 35, 14, 100, 27, 19};
/* Region to invert: 20-30 (inclusive) */
int p[] = {20, 30};
sort_r(arr, 18, sizeof(int), sort_r_cmp, p);
int i;
for(i = 0; i < 18; i++) printf(" %i", arr[i]);
printf("\n");
}
Compile/run/output: 编译/运行/输出:
$ gcc -Wall -Wextra -pedantic -o sort_r sort_r.c
$ ./sort_r
1 2 3 4 5 10 14 18 19 29 28 27 25 21 20 34 35 100
I've tested on mac & linux. 我在mac和linux上测试过。 Please update this code if you spot mistakes / improvement.
如果您发现错误/改进,请更新此代码。 You are free to use this code as you wish.
您可以根据需要自由使用此代码。
For Windows you would use qsort_s
: http://msdn.microsoft.com/en-us/library/4xc60xas(VS.80).aspx 对于Windows,您将使用
qsort_s
: http : //msdn.microsoft.com/en-us/library/4xc60xas( qsort_s
.aspx
Apparently there is some controversy about BSD and GNU having incompatible versions of qsort_r
, so be careful about using it in production code: http://sourceware.org/ml/libc-alpha/2008-12/msg00003.html 显然有一些关于BSD和GNU有
qsort_r
版本不兼容的qsort_r
,所以在生产代码中使用它要小心: http : //sourceware.org/ml/libc-alpha/2008-12/msg00003.html
BTW, the _s
stands for "secure" and the _r
stands for "re-entrant", but both mean that there's an extra parameter. 顺便说一句,
_s
代表“安全”而_r
代表“重入”,但两者都意味着有一个额外的参数。
It's not specified in any portability standard. 它没有在任何可移植性标准中指定。 Also I think it's a mistake to call it a "thread-safe" version of
qsort
. 另外我认为将它称为
qsort
的“线程安全”版本是错误的。 The standard qsort
is thread-safe, but qsort_r
effectively allows you to pass a closure as your comparison function. 标准
qsort
是线程安全的,但qsort_r
有效地允许您传递一个闭包作为比较函数。
Obviously in a single-threaded environment, you can achieve the same result with a global variable and qsort
, but this usage will not be thread-safe. 显然,在单线程环境中,您可以使用全局变量和
qsort
实现相同的结果,但这种用法不是线程安全的。 A different approach to thread-safety would be to use thread-specific data and have your comparison function retrieve its parameter from the thread-specific data ( pthread_getspecific
with POSIX threads, or __thread
variables in gcc and the upcoming C1x standard). 线程安全的另一种方法是使用特定于线程的数据,让比较函数从特定于线程的数据中检索其参数(
pthread_getspecific
使用POSIX线程,或者使用gcc中的__thread
变量和即将推出的C1x标准)。
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