1：qsort函数， return *( int *)b > *(int *)a ? 1 : -1 和 return (( int *)b)[0] > ((int *)a)[0] ? 1 : -1的区别？

2：对加减乘除计算结果有什么影响？哪个正确？

  

[此贴子已经被作者于2017-2-28 15:50编辑过]

设：(int *)b=P

则 1.  *( int *)b      =  *P
   2.  (( int *)b)[0]  =  P[0]

路过

经过试验：

qsort函数， return *( int *)b > *(int *)a ? 1 : -1 ；

排序后，计算正确；

可是，这个代码是完全等价的呀

C标准中有规定： a[i] 等同于 *(a+i)
因此 b[0] 等同于 *(b+0)，等同于 *b

可是，在计算过程中，会出现两种不同的计算结果；只能人工计算判断哪个方法正确了！

例如：


计算结果1               计算结果2
0.855263                1
0.873563                0.837037
0.747126                0.837037
0.955556                1
0.697248                1
0.855263                1
0.747126                1
1                        0.727434
0.873563                1
0.697248                1
               
3.457421                0.997528
1.113855                0.985623
1.188587                0.981072
1.259307                0.973349
1.078908                0.978193
3.137956                0.987309
1.517089                0.993468
2.385143                0.928318
-0.240351                0.973349
1.30704                    0.978193
               
Press any key to continue                Press any key to continue

我觉得  *P 是指当前P  P[0]则是指第一个元素

一样的。

1：如果一样，那么省心不用二选一了；
2：用两个方法分别计算，计算结果不一样；
例如：

方法一：                          方法二：
3.000000  3.000000                        3.000000  3.560000        
                                
0.836066                        0.379747        
0.973958                        0.078947        
0.566474                        0.36611        
0.952919                        0.203273        
0.732824                        0.883402        
0.810247                        0.474474        
0.475907                        0.139676        
0.688853                        0.488304        
1                                0.353742        
0.863686                        0.860957        
                                
4.000000  4.000000(错误！）                        4.000000  2.000000    （正确！）   
                                
0.133929                        0.342857        
0.607143                        0.178571        
0.421053                        0.106667        
0.0058                            0.4        
1                                0.725        
1                                0.833333        
0.1875                            0.256684        
0.003                            0.4        
1                                0.296296        
1                                0.652174        
                                
7.000000  7.000000                        7.000000  3.465753        
                                
0.98926                            2.530189        
0.992717                        1.553683        
0.956527                        1.058629        
0.935797                        1.445122        
0.984023                        1.00839        
0.997038                        20.298866        
0.982813                        3.207247        
0.948814                        2.241864        
0.959189                        -0.202519        
0.984023                        1.009544        
                                
3.250000  3.250000                        3.250000  3.500000        
                                
0.832117                        0.811487        
0.809524                        0.322597        
0.835592                        0.253333        
0.944828                        0.767442        
0.845478                        0.904401        
1                                0.811487        
0.850556                        0.724638        
0.645443                        0.668966        
0.824746                        0.175758        
0.880597                        0.585284        
                                
Press any key to continue                        Press any key to continue        
                                

[此贴子已经被作者于2017-2-28 17:49编辑过]