Question

这是我的第一篇文章。我一直在搜索，但找不到任何有助于解决问题的问题。当我尝试取消引用指针或在函数中应用指针数学时，事情并没有做他们应该做的事情。

例如：*（ptr + a）应该从技术上推进指向我设置的任何值的指针。相反，我只是得到一个错误，上面写着＆＃34;请求会员＆＃39; name＆＃39;在一些不是结构或联合的东西中＃34;这没有任何意义，因为我已经声明并将我的结构指针传递给函数。如果我使用：

＆＃34; start_ptr-＆gt; name.last + a＆＃34;风格，它编译但不排序任何东西。我知道第二个版本在指针数学方面也是不对的。

所以基本上，似乎错误的是编译，看似正确的不是，实际上也没有任何东西。

这是代码

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

/* Structure definition */
/* -------------------- */

struct split
{
    char last[10];
    char first[10];
};

struct info
{
    struct  split name;
    char    address[20];
    char    city[15];
    char    state[3];
    long    zip;
    int     age;
    char    gender;
};  /* end struct info */


void sort_them(struct info *, char); // sort prototype

int main(void)  
{
/* Declare variables */
/* ----------------- */

struct info     people[] =
{

    {"Asimov", "Isaac", "15 Main St", "Worcestor", "MA", 01555, 23, 'M'},
    {"Smith", "Jane", "17 Make Peace", "Wallham", "ND", 10102, 28, 'F'},
    {"De Rippa", "Jack", "18 Able Way ", "Boston", "MA", 50503, 74, 'M'},
    {"Cobb", "Jim", "55 Elm St", "Ware", "MO", 61555, 65, 'M'},
    {"Kapone", "Al", "15 Morin Ave", "Idunno", "MN", 31333, 34, 'M'},
    {"Seigel", "Myron", "44 Wing Blvd West", "Sandwich", "WA", 02537,     21, 'M'},
    {"Thymes", "Mary", "88 Same Place", "Washington", "DC", 90555, 44, 'F'}

};

int             bad_sort;
int             num_people = sizeof(people) / sizeof(people[0]); //this will be the count of how many people there are!
char            sort_order;
char            big_name[22];





struct info *start_ptr = &people[0];
struct info *nums_ptr, *nums_end_ptr = &people[6];
char *big_ptr = &big_name[0];







printf ("\nWelcome to the People Structure Data Report Program\n");



do
{
        bad_sort = 1;

        printf ("\nEnter the sort order for the report: ");
        printf ("\n(N=Name, A=Age, S=State, Z=Zip code ' '=no sort)\n ");

/*               blank or return is allowed for no sorting of the data */

        sort_order = getchar();

        if(sort_order == '\n' || sort_order == ' ') break; 

        sort_order = toupper(sort_order);

        if ((sort_order == 'N') || (sort_order == 'A') || 
                    (sort_order == 'S') || (sort_order == 'Z'))
            bad_sort = 0;
        else
            printf("\nIncorrect Sort order selected, please re-enter:  ");

} while (bad_sort == 1);



switch (sort_order)
{
    case 'N':
        printf("Sort by Name  %i People.\n", num_people); 
        break;
    case 'A':
        printf("Sort by Age  %i People.\n", num_people); 
        break;
    case 'S':
        printf("Sort by State  %i People.\n", num_people); 
        break;
    case 'Z':
        printf("Sort by Zip  %i People.\n", num_people); 
        break;
    default:
        printf("No Sort selected  %i People.\n", num_people); 
        break;
}  /* end cases */

if(sort_order != ' ')
    sort_them (start_ptr, sort_order);


/* Print Report */
/* ------------ */

printf("\n\n                 The People Report\n\n");

printf ("\n\n%-20s%-20s %-15s %-5s %-6s %-3s %-6s", 
        "Name", "Address","City","State","Zip","Age","Gender");

printf ("%-20s%-20s %-15s %-5s %-6s %-3s %-6s\n", 
        "----", "------","----","-----","---","---","------");


for (nums_ptr = start_ptr; nums_ptr <= nums_end_ptr; nums_ptr++, start_ptr++)
{

    strcpy(big_ptr, start_ptr->name.last);
    strcat(big_ptr, ", ");
    strcat(big_ptr,start_ptr->name.first);



    printf ("%-20s%-20s %-15s  %-4s%.5ld    %-3i  %c\n", 
                                                                           big_ptr,start_ptr->address,start_ptr->city,start_ptr->state,start_ptr->zip,
            start_ptr->age,start_ptr->gender);      

} /* end for loop */



printf("\n\n");

return 0;

} /* end main */

void sort_them(struct info *start_ptr, char sort_by)
{
int a,b;
struct info temp;


for(a = 0; a < 6; a++)

    for(b = a + 1; b < 7; b++)
    {
        if(    (sort_by == 'N' && strcmp(start_ptr->name.last + a, start_ptr->name.last + b) > 0)
            || (sort_by == 'A' && start_ptr->age + a > start_ptr->age + b )
            || (sort_by == 'S' && strcmp(start_ptr->state + a, start_ptr->state + b) > 0)
            || (sort_by == 'Z' && (start_ptr->zip + a) > (start_ptr->zip + b) )  
          )


        {
            temp = *(start_ptr + a);
            *(start_ptr + a) = *(start_ptr + b);
            *(start_ptr + b) = temp;

        } /* end if  */


    } /* end inner for loop  */





};









/* end of sort them

Answer 1

我认为以下一行

 strcmp( start_ptr->name.last + a, start_ptr->name.last + b) > 0

应该像下面那样改变

strcmp( (start_ptr + a)->name.last,  
        (start_ptr + b)->name.last  
      ) > 0

以及其他比较。

Answer 2

首先，没有理由不在C：

中使用数组表示法

for(a = 0; a < 6; a++)
for(b = a + 1; b < 7; b++)
{
    if(    (sort_by == 'N' && strcmp(start_ptr[a].name.last, start_ptr[b].name.last) > 0)
        || (sort_by == 'A' && start_ptr[a].age > start_ptr[b].age )
        || (sort_by == 'S' && strcmp(start_ptr[a].state, start_ptr[b].state) > 0)
        || (sort_by == 'Z' && (start_ptr[a].zip) > (start_ptr[b].zip) )  
      )


    {
        temp = start_ptr[a];
        start_ptr[a] = start_ptr[b];
        start_ptr[b] = temp;

    } /* end if  */

表达式start_ptr->name.last + a将start_ptr[0].name.last添加到(ptr+a)并且没有＆＃34;样式＆＃34;指针算术。

如果* ptr指向有效对象，则可以在ptr之前完成指针运算，其中a*sizeof(*ptr)由sizeof(type)提前。否则* ptr会产生段错误（例如，对于ptr = NULL）。然后你可以在我们的示例中使用* ptr：sizeof(struct info)的类型：*(ptr+a)。

基本上ptr[a]与(ptr+a)相同，&ptr[a]为->。

如果您想使用(start_ptr+a)->name运算符，则需要编写

var Person = mongoose.model('Person');
var people = [];

people[0] = new Person({id: 'someid'});
people[0].set('name', 'Mario');
people[1] = new Person({id: 'someid'});
people[1].set('name', 'Mario');
people[2] = new Person({id: 'someid'});
people[2].set('name', 'Mario');

var errors = [];
for(person in people){
 people[person].save(function(err, done){
  if(err) errors.push(err);
  if (person === people.length){ yourCallbackFunction(errors){
    if (errors.length!=0) console.log(errors);
    //yourcode here
   };
  }
 });
}

例如。

为什么我的程序（sort_them函数）没有排序？

2 个答案: