c - 当我尝试在 c 中初始化时的指针

Question

  typedef struct Email
  {
    char  domain [128];
    char  local [128];
  } Email ;

Email email_in(char s[])

{

    Email *result ;

    int c=0;

    for(c=0;c<128;c++)
    {
        result->domain[c]='\0';
        result->local[c]='\0';
    }
    char  *ss = s;//PG_GETARG_CSTRING(0);
    //result = 0;

    int i,j, ind1=0, x=0 , dot=0;
    int length= strlen(ss);
    for(i=0; i<length;i++)
    {

        if(ss[i]<='Z' && ss[i]>='A' )
        {

            ss[i]=ss[i]+32;

        }
    }
    ;

    if ( ((ss[0]<'a') || (ss[0]>'z')) )
    {
        if((ss[0]<'A') || (ss[0]>'Z'))
            perror("Error printed by perror=1");
    }

    else
    {
        for ( i=0;i<length;i++)
        {

            if (ss[i]=='@')
            {
                result->local[i]=ss[i];
                ind1=i+1;
                break;
            }

            else
                if(ss[i]=='-' || ss[i]=='.')
                    if(ss[i-1]=='-' || ss[i-1]=='.')
                    {
                        perror("Error printed by perror=4 ");
                    }
            if ( ((ss[i]<'a') || (ss[i]>'z') )&&((ss[i]<'0')||(ss[i]>'9'))  )
            {
                if(((ss[i]<'A') || (ss[i]>'Z')) &&(ss[i]!='-') &&(ss[i]!='.') )
                {
                    printf("%c \n",ss[i]);
                    perror("Error printed by perror=2");
                }
            }
            if(ss[i]!='@')
                result->local [i]=ss[i];

        }


        for ( j=ind1;j<length;j++)
        {

            if(ss[j]=='.')
                dot= dot+1;

            if(ss[j]=='-' || ss[j]=='.')
                if(ss[j-1]=='-' || ss[j-1]=='.')
                {
                    perror("Error printed by perror=6 ");
                }
            if ( (ss[j]<'a') || ((ss[j]>'z' )  ) )
            {
                if(((ss[j]<'A') || (ss[j]>'Z')) &&(ss[j]!='-') &&(ss[j]!='.') )
                    perror("Error printed by perror=3 ");
            }

            result->domain [x]=ss[j];
            x=x+1;
        }
        result->domain[x+1]='\0';
        result->domain[x]='\0';

        if(dot<1 && dot >2)
            perror("invalid domain");





    }


    return*(result);//PG_RETURN_POINTER(result);
}

void main()
{

    char s1[]="tami@openu.ac.il\0";
    email_in(s1);
    //printf("%s",s1);
}

当它到达 result->domain[c]='\0'; 时显示错误 “reslut=null”

我需要指针来更改原始副本，但该怎么做？ 此函数用于验证 PostgreSQL 中使用的电子邮件地址以添加新数据类型

我对 C 或 C++ 零经验 我需要帮助><

Answer 1

当你做的时候

Email *result ;

您得到一个指向 Email 的指针，但没有得到 Email 变量。

在这种情况下，您应该避免使用指针并直接使用结构。像这样的东西:

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

typedef struct Email
{
    char  domain [128];
    char  local [128];
} Email ;

Email email_in()
{
    Email result;   // Don't use pointer

    strcpy(result.domain, "test_domain");
    strcpy(result.local, "test_local");

    return result;
}

int main(void) {
    Email x=email_in();  // Make the variable x of type Email

    printf("%s\n", x.domain);
    printf("%s\n", x.local);

    return 0;
}

如果您更喜欢使用指针，您可以尝试类似的方法:

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

typedef struct Email
{
    char  domain [128];
    char  local [128];
} Email ;

Email* email_in()
{
    Email* result;
    result = malloc(sizeof(Email));  // Allocate memory for an Email and make result point to it

    strcpy(result->domain, "test_domain");
    strcpy(result->local, "test_local");

    return result;
}

int main(void) {
    Email* x=email_in();  // Make the variable x of type pointer to Email

    printf("%s\n", x->domain);
    printf("%s\n", x->local);

    free(x);              // Free the allocated memory

    return 0;
}