user-0 提问: C语言函数qsort中compare详细用法

回复:
user: user-1
content: int compare (const void *p, const void *q) {     /*int x = *(const int *)p;     int y = *(const int *)q;     if (x < y) {         return -1;         如果x<y那么返回-1     } else if (x > y) {         return 1;         如果x>y那么返回1     }     return 0;*/           相等等于0 return (*(int *)p-*(int *)q); } 这个函数就是利用返回值来查看x和y的大小关系 调用compare函数后，如果返回值是 -1那么x<y 1那么x>y 0那么相等。 函数返回值做验证参数

user: user-2
content: 应该说是一样的，这个compare函数就是告诉它两个数的大小关系就行

user: user-3
content: 参考C:\Program Files\Microsoft Visual Studio 10.0\VC\crt\src\qsort.c

user: user-3
content: 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