如何用C语言编辑文件

Question

我是C的新手，正在尝试为酒店编写程序，让客户编辑他们的预订详细信息，如名字、姓氏。。。等等。我写的代码可以运行，但文件中的数据不被编辑。

当我输入错误的用户名和密码时，("Record not found! Please enter your Username and Password again.n");行的else语句也不会打印出来。

到目前为止，我得到的是：

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h> 
#include <string.h>  
#include <stdbool.h>
struct customer_details  // Structure declaration
{
char uname[100];
char pass[100];
char fname[100];
char lname[100];
char ic[100];
char contact[100];
char email[100];
char room[100];
char day[100];
}s;

void main()
{
FILE* f, *f1;
f = fopen("update.txt", "r");
f1 = fopen("temp.txt", "w");
char uname[100], pass[100];
int valid = 0;
// validate whether file can be opened.
if (f == NULL)
{
printf("Error opening file!n");
exit(0);
}
printf("Please enter your Username and Password to update your booking detail.n");
printf("nUsername: ");
fgets(uname, 100, stdin);
uname[strcspn(uname, "n")] = 0;
printf("Password: ");
fgets(pass, 100, stdin);
pass[strcspn(pass, "n")] = 0;
while (fscanf(f, "%s %s", s.uname, s.pass) != -1)
{
if (strcmp(uname, s.uname) == 0 && strcmp(pass, s.pass) == 0)
{
valid = 1;
fflush(stdin);
printf("Record found!n");
printf("nEnter First Name: ");
scanf("%s", &s.fname);
printf("nEnter Last Name: ");
scanf("%s", &s.lname);
printf("nEnter IC Number: ");
scanf("%s", &s.ic);
printf("nEnter Contact Number:");
scanf("%s", &s.contact);
printf("nEnter Email: ");
scanf("%s", &s.email);
printf("nEnter Room ID :");
scanf("%s", &s.room);
printf("nEnter Days of staying:");
scanf("%s", &s.day);
fseek(f, sizeof(s), SEEK_CUR); //to go to desired position infile
fwrite(&s, sizeof(s), 1, f1);
}
else
("Record not found! Please enter your Username and Password again.n");
}
fclose(f);
fclose(f1);
if (valid == 1)
{

f = fopen("update.txt", "r");
f1 = fopen("temp.txt", "w");
while (fread(&s, sizeof(s), 1, f1))
{
fwrite(&s, sizeof(s), 1, f);
}
fclose(f);
fclose(f1);
printf("Record successfully updated!n");
}
}

update.txt文件包含以下内容：

abc 123倒数第一234 [e-mail]101 3

Answer 1

您忘记了printf调用，请更改

("Record not found! Please enter your Username and Password again.n");

至

printf("Record not found! Please enter your Username and Password again.n");

如果你编译你的程序时启用了警告，你应该得到一个类似的警告

t.c:68:12: warning: statement with no effect [-Wunused-value]
("Record not found! Please enter your Username and Password again.n");
^