c语言关于函数指针里面用void*传参数的问题

[遇女心静]

(1)我定义这样一个函数void insertionSort(int (*comp)(void*,void*))；
(2)写了一个函数
int intGreater(int *x,int *y){
return *x-*y;
}
（3）调用的时候insertionSort(intGreater);
会报错：“insertionSort”: 不能将参数 1 从“int (__cdecl *)(int *,int *)”转换为“int (__cdecl *)(void *,void *)”

[常书]

可以将 int intGreater(int *x,int *y){ return *x-*y; } 定义为 int intGreater(void *x,void *y){ return *(int*)x-*(int*)y; }

[遇女心静]

引用 1 楼 r_Jimy 的回复:

可以将 int intGreater(int *x,int *y){ return *x-*y; } 定义为 int intGreater(void *x,void *y){ return *(int*)x-*(int*)y; }

--------------------- 可以是可以，但是比如要要比较double类型的话，函数也是int doubleGreater(void *x,void *y),只能靠函数名区别了，我想传入参数的时候就限定。

[勤奋的小游侠]

typedef int (*func)(void*,void*) insertionSort((func)intGreater);//强制类型转换

[ParsifalC]

int (*comp)(void*,void*) int intGreater(int *x,int *y) 这是两种不同的函数指针类型。 一楼说的方法是正确的做法。 在具体的回调函数内部进行类型转换，这样才能发挥回调函数的优势。 在不更改调用方的代码情况下，实现不同的功能。

[遇女心静]

引用 3 楼 lovesmiles 的回复:

typedef int (*func)(void*,void*) insertionSort((func)intGreater);//强制类型转换

谢谢大神，应该强转一下，测试是没问题的。

[遇女心静]

引用 4 楼 ParsifalC 的回复:

int (*comp)(void*,void*) int intGreater(int *x,int *y) 这是两种不同的函数指针类型。 一楼说的方法是正确的做法。 在具体的回调函数内部进行类型转换，这样才能发挥回调函数的优势。 在不更改调用方的代码情况下，实现不同的功能。

嗯，一楼方法是可以的，但是就是我要有DOUBLE类型比较，方法的参数都是void*，只能再函数体里面转换，4楼的方法比较好

[赵4老师]

qsort
Performs a quick sort.

void qsort( void *base, size_t num, size_t width, int (__cdecl *compare )(const void *elem1, const void *elem2 ) );

Routine Required Header Compatibility 
qsort <stdlib.h> and <search.h> ANSI, Win 95, Win NT 


For additional compatibility information, see Compatibility in the Introduction.

Libraries

LIBC.LIB Single thread static library, retail version 
LIBCMT.LIB Multithread static library, retail version 
MSVCRT.LIB Import library for MSVCRT.DLL, retail version 


Return Value

None

Parameters

base

Start of target array

num

Array size in elements

width

Element size in bytes

compare

Comparison function

elem1

Pointer to the key for the search

elem2

Pointer to the array element to be compared with the key

Remarks

The qsort function implements a quick-sort algorithm to sort an array of num elements, each of width bytes. The argument base is a pointer to the base of the array to be sorted. qsort overwrites this array with the sorted elements. The argument compare is a pointer to a user-supplied routine that compares two array elements and returns a value specifying their relationship. qsort calls the compare routine one or more times during the sort, passing pointers to two array elements on each call:

compare( (void *) elem1, (void *) elem2 );

The routine must compare the elements, then return one of the following values:

Return Value Description 
< 0 elem1 less than elem2 
0 elem1 equivalent to elem2 
> 0 elem1 greater than elem2 


The array is sorted in increasing order, as defined by the comparison function. To sort an array in decreasing order, reverse the sense of “greater than” and “less than” in the comparison function.

Example

/* QSORT.C: This program reads the command-line
 * parameters and uses qsort to sort them. It
 * then displays the sorted arguments.
 */

#include <stdlib.h>
#include <string.h>
#include <stdio.h>

int compare( const void *arg1, const void *arg2 );

void main( int argc, char **argv )
{
   int i;
   /* Eliminate argv[0] from sort: */
   argv++;
   argc--;

   /* Sort remaining args using Quicksort algorithm: */
   qsort( (void *)argv, (size_t)argc, sizeof( char * ), compare );

   /* Output sorted list: */
   for( i = 0; i < argc; ++i )
      printf( "%s ", argv[i] );
   printf( "\n" );
}

int compare( const void *arg1, const void *arg2 )
{
   /* Compare all of both strings: */
   return _stricmp( * ( char** ) arg1, * ( char** ) arg2 );
}


Output

[C:\code]qsort every good boy deserves favor
boy deserves every favor good


Searching and Sorting Routines

See Also   bsearch, _lsearch