c - 使用 C 验证文件中的登录凭据

Question

我的程序应该检查凭据是否存在于创建的“MyDetails.txt”文件中，如果是，则允许用户继续，否则终止。但是，该程序接受传递给它的任何值并重写现有数据。 我想找出代码中存在哪些错误以及是否有其他替代方法可以解决它。(验证文件中的凭据)。 下面是该程序的代码。

#include<stdio.h>
#include<string.h>
#include<conio.h>
#include <stdlib.h>
main()
{
FILE *Credentials;
char username[15];
char password[12];

//open file for writing
Credentials  =fopen("MyDetails.txt","w");
//check if file exists
if(Credentials == NULL)
{
    printf("File does not exist\n");
    return;
}
//New User
printf("Enter Username\n");
scanf("%s",&username);
fprintf(Credentials,"Username:%s\n",username);

printf("Enter Password\n");
scanf("%s",&password);
fprintf(Credentials,"Password:%s\n",password);

    if(username==username)
    {
    if(password=password)
    {
    printf("Login Successfull\n");  

    printf("\n");

    float result;
    int choice,num;
    printf("Press 1 to Exit\n");
    printf("Press 2 to Input Current Reading\n");
    printf("Press 3 to Calculate Bill\n");
    printf("Press 4 to Make Payment\n");
    choice = input();
    float current,rate,previous,units,monthly,bill,stand,paid;
    switch (choice){
    case 1:{
    exit(0);
    break;
    }

    case 2:{
    printf("Input Current Reading\n");
    scanf("%f",&current);

    }

    case 3:{
    printf("Enter Rate\n");
    scanf("%f",&rate);
    printf("Enter Previous Reading\n");
    scanf("%f",&previous);


    units=current-previous;   
    monthly=units*rate;                 
    bill=150+monthly;

    printf("\n Total Bill:%.3f\n",bill);


    }
    case 4:{
    printf ("------PAYMENT------\n");
    printf("\n");
    printf("Amount To Pay is %.3f",bill);
    printf("\n");
    printf("Enter Amount\n");
    scanf("%f",&paid);
    printf("Remaining Balance\n %.3f",bill-paid);
    break;
    }   
    }
    }
    else
    {
    printf("\n Wrong Password");
    }
    }
    else
    {
    printf("\n User Doesn't Exist'");
    }
    return 0;
    }
    int input()
    {
    int number;
    scanf("%d",&number);
    return (number);
    }

    void output(float number)
    {
    printf("%f",number);
    }           

Answer 1

首先，您将用户名与其自身进行比较。显然，这始终是“真实”的结果。^†

您应该将文件中的用户名读取到一个变量中，然后将用户输入到另一个变量中，并比较这两个不同变量.

其次，你需要了解how to properly compare character arrays .

_{^† 有时这不是真的，例如比较 NaN 值，但这不是其中之一!}