Question

做这个简单的程序。这只是银行服务计划的第五部分。不知怎的，我被这个fread()困住了。我无法比较用户和我的数据库的输入。当我的程序启动时，在我输入用户并传递它有点“挂起”或“冻结”之后会出现一个弹出窗口并显示“结束程序”。顺便说一下，我正在使用Dev C ++。

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

struct client
{
    char accnum[9];
    char accode[5];
    char fname[20];
    char lname[20];
}s;




main()
{
    FILE *fp;

    char user[9];
    char pass[5];

    fp=fopen("account.txt","a");
    if(fp!=NULL)
    {
        /**
        strcpy(s.accnum,"abcd1234");
        strcpy(s.accode,"1234");
        strcpy(s.fname,"john");
        strcpy(s.lname,"doe");      
        fwrite(&s,sizeof(s),1,fp);
        **/

        printf("BANKING SERVICE");
        printf("\nInput User: ");
        gets(user);

        printf("\nInput Pass: ");
        gets(pass);


        while(!feof(fp))
        {
                while(fread(&s,sizeof(s),1,fp)==1);
                {


                    if(ferror(fp))
                    {
                        printf("error");
                    }
                    if (strcmp(user,s.accnum) == 0 && strcmp(pass,s.accode) == 0)
                    {
                        printf("\n\nsuccess!");
                    }

                    else 
                    {
                                printf("\n\nerror!");
                    }

                }
        }

        fclose(fp);
    }






    fclose(fp);
    getch();
}

Answer 1

在循环检查中是否成功匹配。如果未找到匹配项，则found标记仍为零。然后在while循环完成后报告问题 fgets将包含换行符，因此在与文件内容进行比较之前必须将其删除，因为注释部分不显示任何换行符。

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

struct client
{
    char accnum[9];
    char accode[5];
    char fname[20];
    char lname[20];
}s;

int main()
{
    FILE *fp;
    int found = 0;
    char user[20];//allow extra
    char pass[20];

    fp=fopen("account.txt","a");
    if(fp==NULL)
    {
        perror ("could not open file ");
        return 1;
    }
    /**
    strcpy(s.accnum,"abcd1234");
    strcpy(s.accode,"1234");
    strcpy(s.fname,"john");
    strcpy(s.lname,"doe");
    fwrite(&s,sizeof(s),1,fp);
    **/
    printf("BANKING SERVICE");
    printf("\nInput User: ");
    fgets(user, sizeof ( user), stdin);
    if ( user[strlen(user)-1] == '\n') {
        user[strlen(user)-1] = '\0';//remove newline
    }
    printf("\nInput Pass: ");
    fgets(pass, sizeof ( pass), stdin);
    if ( pass[strlen(pass)-1] == '\n') {
        pass[strlen(pass)-1] = '\0';//remove newline
    }
    while(fread(&s,sizeof(s),1,fp)==1)
    {
        if (strcmp(user,s.accnum) == 0 && strcmp(pass,s.accode) == 0)
        {
            printf("\n\nsuccess!");
            found = 1;
            break;
        }
    }
    if ( found == 0)
    {// after entire file has been read, report problem
        printf("\n\nno match for that account and passcode!");
    }
    fclose(fp);
    getchar();
    return 0;
}

Answer 2

您需要检查文件的结尾。

while( !feof( fp ) )
{
   fread(&s,sizeof(s),1,fp);
   if( ferror( fp ) )
   {
     // Error occurred
     break;
   }

   if (strcmp(user,s.accnum) == 0 && strcmp(pass,s.accode) == 0)
   {
       printf("\n\nsuccess!");
   }
   else 
   {
       printf("\n\nerror!");
   }
}

C中的文件处理（使用fread＆amp; fwrite）

2 个答案: