Basic rename statements's unusal behaviour in c

Question

I am working on a inventory management project in c. In the project I need to delete records.

I have found out that to do this delete record work I have to search the specific record and write the other records to a temp file and the rename it to the original filename just after deleting the original file. But in my project code somehow the rename statement is skipping.

This is my project code:

#include<stdio.h>
#include <string.h>
#include <stdlib.h>
#include<inttypes.h>
#include<windows.h>
struct record_stu
{
    unsigned long long int id;
    int gm;
    char subject[255],s[255],y[255];

};
main()
{
    struct record_stu st;
    FILE *fp,*fp_tmp;
    char c,subject[255],year[255],semester[255];
    unsigned long long int id;
    int gm,j,z;
    int records=0;
    const char* charString1 = "Student_ID";
    const char* charString2 = "Subject";
    const char* charString3 = "Year";
    const char* charString4 = "Semester";
    const char* charString5 = "Gained_Marks";
    const char* charString6 = "Yes";
    const char* charString7 = "No";
    //const char* charString8 = "CSE-4year1.dat";
    
    fp = fopen("CSE-4Year1.dat","r");
    if(!(fp))
    {
      printf("An Error has occurred.Department can't be Found\n");
    }
    else
    {
      printf("Department Found.\n");
      printf("Select a Specific Record to Delete!");
      printf("\nEnter Student ID\n");
      scanf("%"PRIu64"",&id);
      printf("\nEnter subject\n");
      scanf("%s",subject);
      printf("\nEnter Year\n");
      scanf("%s",year);
      printf("\nEnter Semester\n");
      scanf("%s",semester);
      printf("%s\t%s\t%s\t%s\t%s\n",charString1,charString2,charString3,charString4,charString5);
      rewind(fp);
      while (!feof(fp))
      {
        fscanf(fp,"%11"PRIu64"\t%3s\t%3s\t%3s\t%10d", &st.id, &st.subject, &st.y, &st.s,&st.gm);
        records++;
        fp_tmp = fopen("temp.dat","a");
        if(st.id==id)
        {
          if(strcmp(st.subject,subject)==0)
          {
            if(strcmp(st.y,year)==0)
            {
              if(strcmp(st.s,semester)==0)
              {
                printf("%11"PRIu64"\t%3s\t%3s\t%3s\t%10d\n", st.id,st.subject, st.y, st.s, st.gm);
                printf("Are Sure You Want This Record to be Deleted?(Yes(1)/No(2))\n");
                scanf("%d",&z);
                if(z==1)
                {
                  printf("%11"PRIu64"\t%3s\t%3s\t%3s\t%10d\n", st.id,st.subject, st.y, st.s, st.gm);
                }
                else if(z==2)
                {
                  break;
                }
                else
                {
                  printf("Wrong Input.Pleas check case of your input.\n");
                  break;
                }
              }
            }
          }
         }
         else
         {
           fprintf(fp_tmp,"%11"PRIu64"\t%3s\t%3s\t%3s\t%10d\n", st.id, st.subject, st.y, st.s,st.gm);
         }
        }
       }
       fclose(fp);
       fclose(fp_tmp);
       remove("CSE-4Year1.dat");
       if (rename("temp.dat","CSE-4Year1.dat") == 0)
       printf("Renamed successfully");
       else
       printf("Unable to rename the file");
       break;

The funny thing is I have a small code to rename that's working fine. Although the small code and project code has basically the same syntax.

The small code is here:

#include<stdio.h>
main()
{
 //remove("b.txt");
 rename("temp.dat","CSE-4Year1.dat");
}

Which of the two messages was printed after testing `rename` result? — Weather Vane, Aug 05 '17 at 16:55
Actually I wanted the "temp.dat" file renamed to "CSE-4Year1.dat" but that statement doesn't even execute. I used a if/else condition to verify if the file has been renamed or not. — Khandkar Asif Hossain, Aug 05 '17 at 16:56
So, *which* message was printed? One of them must have been. If successful the new file is `a.dat` not the `CSE-4Year1.dat` in your "small code". Aside: I advise you to include a final `\n` newline at the end of such progress messages. — Weather Vane, Aug 05 '17 at 16:57
The small code works fine. But the large project code doesn't. That's the problem here. @Weather Vane — Khandkar Asif Hossain, Aug 05 '17 at 17:00
Please read the comments again, carefully. Does `a.dat` exist? — Weather Vane, Aug 05 '17 at 17:01
I already tried that @xing. Nothing seems to happed I am afraid. — Khandkar Asif Hossain, Aug 05 '17 at 17:01
Nothing seems to happen. Not even one of the two possible messages? — Weather Vane, Aug 05 '17 at 17:02
I have read the comments. And sorry to say a.dat doesn't exists I am afraid @WeatherVane — Khandkar Asif Hossain, Aug 05 '17 at 17:02
In the large code both possibilities are not working @WeatherVane — Khandkar Asif Hossain, Aug 05 '17 at 17:03
For the last time: **which message was printed** (after adding a newline to the output)? — Weather Vane, Aug 05 '17 at 17:03
If `rename` fails one possible reason is that `a.dat` already exists (which you deny). Be a sport, and change `a.dat ` to `CSE-4Year1.dat` to match your small test. — Weather Vane, Aug 05 '17 at 17:08
Sorry but I have and re checked that "a.dat" doesn't exist in my directory. And the large code works file until the remove statement. And I am telling the truth. What reason do I have to lie to you guys?@WeatherVane — Khandkar Asif Hossain, Aug 05 '17 at 17:12
Sorry to say that the large code see is just a minimal part of my full code. I can provide you the full code if you want to check. @iBug — Khandkar Asif Hossain, Aug 05 '17 at 17:15
I have just tried the five lines of your code from `remove("CSE-4Year1.dat");` onwards and they do what is expected. If `a.dat` does not exist I get `Renamed successfully` but if it does I get `Unable to rename the file`. I am still mystifed why you persist with `a.dat` when the small example (and as should plainly be in the big code) uses `CSE-4Year1.dat`. — Weather Vane, Aug 05 '17 at 17:19
Manually deleted the file and the file do get created again but renaming process doesn't work. @xing — Khandkar Asif Hossain, Aug 05 '17 at 17:19
Sorry but I have tried "CSE-4Year1.dat" as you suggested. But again the code works until remove statement and shows "unable to rename the file".@WeatherVane — Khandkar Asif Hossain, Aug 05 '17 at 17:22
Okay guys. Why are you guys down voting this question. Have you executed this code and been successful renaming the "temp.dat" file to "CSE-4Year1.dat"? — Khandkar Asif Hossain, Aug 05 '17 at 17:25
Have you created a [mcve]? Also, [`while (!feof(fp))` is wrong](https://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong). — melpomene, Aug 05 '17 at 17:26
No I have just compiled it but it is incomplete so will not compile. As I said previously, I made a small program of the 5 lines I mentioned: they work. Are you seriously expecting us to build a data base with all those entries? — Weather Vane, Aug 05 '17 at 17:26
I downvoted in exasperation because you did not explain why you delete one file but then rename to a different name `a.dat` contrary to the small test. — Weather Vane, Aug 05 '17 at 17:29
No absolutely not. But did you used switch in your small program. I have created that small code to regenerate the temp.dat to CSE-4Year1.dat using completely different c program file. But I need to do that in the large code. @WeatherVane — Khandkar Asif Hossain, Aug 05 '17 at 17:33
So *why* did you rename `temp.dat` to `a.dat` after deleting `CSE-4Year1.dat`? — Weather Vane, Aug 05 '17 at 17:34
Of course I did. it say's "Provide minimal code to reproduce the same problem you are facing. So that busy people of this site can quickly come up with an answer to your problem and help to keep the website clean and informative" @melpomene — Khandkar Asif Hossain, Aug 05 '17 at 17:35
I already said the "a.dat" file doesn't even generate. Besides I have already edited that part of the code as you suggest to enhance understability of the large code.@WeatherVane — Khandkar Asif Hossain, Aug 05 '17 at 17:37
@melpomene also advised reading [Why is “while ( !feof (file) )” always wrong?](https://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong). — Weather Vane, Aug 05 '17 at 17:38
Furthermore the code is poorly formatted so is very difficult to read. You are asking us to read code that cannot easily be read, cannot be compiled, and requires an understanding and entry of multiple inputs to test. Impossible - hence the DV. — Weather Vane, Aug 05 '17 at 17:44
"while(!eof) is wrong because it tests for something that is irrelevant and fails to test for something that you need to know. The result is that you are erroneously executing code that assumes that it is accessing data that was read successfully, when in fact this never happened." I get it. But I need to check until "end of file" for data. But when I use "While(fp!=EOF)" the large code executes but never terminates.@WeatherVane — Khandkar Asif Hossain, Aug 05 '17 at 17:48
Thanks a lot. the while condition did work and showed "deleted Successfully". But for some reason the file become insanely large for my inputs. Around 182 mb and on top of that I can't even open the file now. @xing — Khandkar Asif Hossain, Aug 05 '17 at 17:55
Thanks again for that awesome while condition. But It seems to delete some records that it wasn't suppose to. @Barmar — Khandkar Asif Hossain, Aug 05 '17 at 18:00

Khandkar Asif Hossain · Accepted Answer · 2019-05-26T14:11:01.997

Here is the complete code. The renaming problem is gone. The renaming problem occurs if the the file is open or doesn't exists in the directory.

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

//Variable Declarations
struct record_stu st;
FILE *fp,*fp_tmp,*fp1,*f,*f1;
unsigned long long int id;
char Selected_Exam[255],subject[255],Exam[255],year[255];
char semester[255],Dept_name[255],username[55],username_log[55], pass1[8]; 
char pass2[8],pasword[10],usrname[10],ch,pasword1[10];
char usrname1[10],Course_Code[255],ss[255],s1[255] = "";
char s2[255] = "",Gained_Letter_Grade[255],filename,lg,ct[255],cc[255],ct1[255];
int Course_Code_Number,i,gm,j=0,z,n=0,i,cs=0;
int flag=0,records=0,x[12],Dept_code,Gained_Mark,p=0;
float Gained_Grade_Point,Credit_Completed,gp,cd,tgp=0,tcd=0,cgpa=0,sgpa,pgp,ccr;

const char* charString1 = "Exam";
const char* charString2 = "Student_ID";
const char* charString3 = "Department Name";
const char* charString4 = "Course Code";
const char* charString5 = "Year";
const char* charString6 = "Semester";
const char* charString7 = "Letter Grade";
const char* charString8 = "Gained Mark";
const char* charString9 = "Grade Point";
const char* charString10 = "Credit Completed";
const char* charString11 = "Course Title";
const char* charString12 = "Yes";
const char* charString13 = "No";

struct record_stu
{
 unsigned long long int id;
 float sgpa;
 int gm;
 float gp,cd,ccr;
 char Exam[255],subject[255],semester[255],year[255];
 char Dept_name[255],Exam1[255],lg[255],ct[255],cc[255],ct1[255];
};
//Variable Declarations    
main()
{
 //File open command
 fp = fopen("Student - Copy.txt","r");
 fp_tmp = fopen("temp.txt","w");
 //File Open Command

 if(!(fp)) //File Open Error Detection
 {
   printf("An Error has occurred.File can't be Found\n");
 }
 else //Searching for the record to delete
 {
   fclose(fp_tmp);
   fclose(fp);
   printf("File Found.\n");
   rewind(fp);
   printf("\nEnter Student ID: ");
   scanf("%"PRIu64"",&id);
   printf("\nEnter Course Code:");
   scanf("%s",subject);

   fp = fopen("Student - Copy.txt","r");
   fp_tmp = fopen("temp.txt","w");
   while (fscanf(fp,"%s %"PRIu64"%s%s%s%s%s%d%f%f%s\n",st.Exam1,&st.id,st.Dept_name,st.subject,st.year,st.semester,&st.lg,&st.gm,&st.gp,&ccr,&st.ct1) != EOF)
      {
        records++;
        if(st.id==id && strcmp(st.subject,subject)==0)
        {
          printf("Do you want to delete the record?(Yes(1)/No(2))\nEnter Your Choice: ");
          scanf("%d",&z);
          printf("Confirmation Code = %d\n",z);
          if(z==1)
          {
             printf("Do you want to confirm deletion of the record?(Yes(1)/No(2))\nEnter Your Choice: ");
              scanf("%d",&p);
          }
        }
        else
        {
             fprintf(fp_tmp,"%s %11"PRIu64"\t%s\t%s\t%3s\t%3s\t%s\t%d\t%3.2f\t%f\t%s\n",st.Exam1,st.id,st.Dept_name,st.subject,st.year,st.semester,st.lg,st.gm,st.gp,ccr,st.ct1);
        }
        }


    }//Searching for the record to delete

    //Actual Delete operation by renaming the temporary file to the source file name
    if(p==1)
    {
        printf("Confirmation Code = %d\n",p);
        fclose(fp_tmp);
        fclose(fp);
        remove("Student - Copy.txt");
        if(rename("temp.txt","Student - Copy.txt")==0)
            printf("Delete Successful");
    }
    else
    {
        fclose(fp_tmp);
        fclose(fp);
        printf("Delete Unsuccessful");
        remove("temp.txt");
    }
    //Actual Delete operation by renaming the temporary file to the source file name
}

2

Please add some comment – Wang Liang May 26 '19 at 14:03

Basic rename statements's unusal behaviour in c

1 Answers1