[英]Variadic function in C99 to deallocate several arrays?
Currently, I have a very simple function to deallocate array of doubles in my program: 当前,我有一个非常简单的函数来在程序中释放双精度数组:
void deallocate(double** array)
{
free(*array);
}
I would like this function to be variadic in order to take several arrays, and free them one after another. 我希望此函数可变,以便采用多个数组,并一个接一个地释放它们。 I've never written a variadic function, and as there may exist tricks with pointers I would like to know how to do that.
我从未写过可变参数函数,由于可能存在一些使用指针的技巧,我想知道如何做到这一点。
Don't do this with a variadic function, this concept should be retired. 不要通过可变函数来执行此操作,这个概念应该被淘汰。 In particular it makes no sense at all for something that is to receive arguments of all the same type,
void*
. 特别是对于要接收所有相同类型的参数
void*
东西根本没有任何意义。
Just have a simple function, first that receives an array of pointers 只是有一个简单的函数,首先接收一个指针数组
void free_arrays(void* a[]) {
for (size_t i = 0; a[i]; ++i) free(a[i]);
}
Then you can wrap that with a macro like that 然后可以用这样的宏将其包装
#define FREE_ARRAYS(...) free_arrays((void*[]){ __VA_ARGS__, 0 })
This supposes that none of your pointers is already 0
, since the processing would stop at that point. 假设您的所有指针都不是
0
,因为处理将在该点停止。
If you'd have a need to have that working even if some of the pointers are 0
, you'd have to pass the number of elements as a first parameter to your function. 如果即使某些指针为
0
,也需要使它工作,则必须将元素数量作为第一个参数传递给函数。 This is a bit tedious but can be determined in the macro, too. 这有点乏味,但是也可以在宏中确定。
void free_arrays0(size_t n, void* a[]) {
for (size_t i = 0; i < n; ++i) free(a[i]);
}
#define FREE_ARRAYS0(...) \
free_arrays( \
sizeof((void*[]){ __VA_ARGS__})/sizeof(void*), \
(void*[]){ __VA_ARGS__} \
)
You can do it like this: 您可以这样做:
void deallocate(double *p, ...)
{
va_list ap;
va_start(ap, p);
do {
free(p);
p = va_arg(ap, double *);
} while (p);
va_end(ap);
}
Call as deallocate(p1, p2, p3, (double *)NULL)
. 调用为
deallocate(p1, p2, p3, (double *)NULL)
。 You need the NULL
(or some other value) as a sentinel to signal the end of the argument list; 您需要将
NULL
(或其他某个值)作为标记来表示参数列表的结尾; none of the other pointers should be NULL
or the loop will stop prematurely. 其他指针都不应该为
NULL
否则循环将过早停止。
I'm not saying that this is a good idea, though: varargs functions have their use cases, but they're error-prone with pointers because some implicit conversions don't take place (because the compiler doesn't know the type of the arguments beyond the first). 我并不是说这是个好主意:varargs函数有其用例,但它们很容易出现指针错误,因为某些隐式转换不会发生(因为编译器不知道超出第一个的论点)。
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