您为什么不需要将参数传递给qsort比较器函数? [英] Why don't you need to pass arguments to a qsort comparator function?
问题描述
以下代码摘自此处.
* qsort example */
#include <stdio.h>
#include <stdlib.h>
int values[] = { 40, 10, 100, 90, 20, 25 };
int compare (const void * a, const void * b)
{
return ( *(int*)a - *(int*)b );
}
int main ()
{
int n;
qsort (values, 6, sizeof(int), compare);
for (n=0; n<6; n++)
printf ("%d ",values[n]);
return 0;
}
我们有一个带有签名的参数的compare函数,但是当我们在qsort中调用它时,不会传递任何参数. a
和b
的值如何传递给函数?谢谢
We have a compare function with parameters in its signature but when we call it in qsort no arguments are passed. How are the values of a
and b
passed to the function? Thanks
推荐答案
在此表达式的上下文中:
In the context of this expression:
qsort (values, 6, sizeof(int), compare);
标识函数的子表达式compare
衰减为指向该函数的指针(而不是函数调用).该代码实际上等效于:
the subexpression compare
that identifies a function decays into a pointer to that function (and not a function call). The code is effectively equivalent to:
qsort (values, 6, sizeof(int), &compare);
当用作函数的参数时,这与数组发生的事情是完全相同的(您可能之前见过,但更经常被问到):
This is exactly the same thing that happens to arrays when used as arguments to a function (which you might or not have seen before but is more frequently asked):
void f( int * x );
int main() {
int array[10];
f( array ); // f( &array[0] )
}
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