c - Modify an existing line in file and trim the rest of the line

Question

Please help me, I made a function to modify a line in file using C language. Now my problem is that although the line is modified, the rest of the line I modified is still as is; For example if the new data I enter is shorter than the original line, my new data will be written, but the rest of the line will still be filled with old data. Please check the first line in the outputs below. Please advise me, thank you very much.

Original file:

Sam,Thomas,10-06-1995,26 Elhoreya Street,01234567899,[email protected]
Steven,Thomas,10-06-1995,26 Elhoreya Street,01234567899,[email protected]

Expected output file:

John,George,12-1-2000,23 MN Street,1234567899,[email protected]
Steven,Thomas,10-06-1995,26 Elhoreya Street,01234567899,[email protected]

Real output file:

John,George,12-1-2000,23 MN Street,1234567899,[email protected]@gmail.com
Steven,Thomas,10-06-1995,26 Elhoreya Street,01234567899,[email protected]

This is my function:

void modify(contact c[])
{
    int flag=0, k=0, count_matches=0, match_cont_pos[100], choose;
    char name[50], temp;

    FILE * file;
    file = fopen("info.txt", "rb+");

    if(file == NULL)
    {
        printf("Error opening file
");
        exit(1);
    }

    else
    {
        printf("
Enter the name you want to search: ");
        scanf("%s",&name);

        for(int j = 0; name[j] != ''; j++)
            name[j] = tolower(name[j]);

        for(int i = 0; i < count ; i++) {

            for(int j = 0; c[i].last_name[j] != ''; j++)
                c[i].last_name[j] = tolower(c[i].last_name[j]);

            if(strcmp(c[i].last_name,name) == 0)
            {
                match_cont_pos[k]=i;
                k++;
            }

        }
        for(int d=0;d<k;d++)
            printf("match pos %d
",match_cont_pos[d]);

        for(int d=0;d<k;d++){
            printf("
%s
%s
%d %d %d
%s
%d
%s

", c[match_cont_pos[d]].last_name,c[match_cont_pos[d]].first_name,c[match_cont_pos[d]].DoB.day,c[match_cont_pos[d]].DoB.month,c[match_cont_pos[d]].DoB.year,c[match_cont_pos[d]].street_address,c[match_cont_pos[d]].phone_number,c[match_cont_pos[d]].email);
        }

        if(k>1){

            printf("Enter the number of the record you want to modify: ");
            scanf("%d",choose);

            printf("Enter last name: ");
            scanf("%s",&c[match_cont_pos[choose-1]].last_name);
            printf("Enter first name: ");
            scanf("%s",&c[match_cont_pos[choose-1]].first_name);
            printf("Enter phone number: ");
            scanf("%d",&c[match_cont_pos[choose-1]].phone_number);
            printf("Enter email: ");
            scanf("%s",&c[match_cont_pos[choose-1]].email);
            printf("Enter birth date: ");
            scanf("%d %d %d",&c[match_cont_pos[choose-1]].DoB.day,&c[match_cont_pos[choose-1]].DoB.month,&c[match_cont_pos[choose-1]].DoB.year);
            printf("Enter the address: ");
            scanf("%c",&temp); // temp statement to clear buffer
            scanf("%[^
]",&c[match_cont_pos[choose-1]].street_address);

            fseek(file,-sizeof(c),SEEK_SET);

            fprintf(file,"%s,%s,%d-%d-%d,%s,%d,%s",c[match_cont_pos[choose-1]].last_name,c[match_cont_pos[choose-1]].first_name,c[match_cont_pos[choose-1]].DoB.day,c[match_cont_pos[choose-1]].DoB.month,c[match_cont_pos[choose-1]].DoB.year,c[match_cont_pos[choose-1]].street_address,c[match_cont_pos[choose-1]].phone_number,c[match_cont_pos[choose-1]].email);
        }

    }
    fclose(file);
}

question from:https://stackoverflow.com/questions/65837494/modify-an-existing-line-in-file-and-trim-the-rest-of-the-line

Answer 1

Consider these suggestions, they are to lead you towards an answer:

• Your file is like a byte array, modifying some bytes in the middle does not change the position of the remaining bytes in the file.
• You may be overwriting part of one line and leaving extra characters from the old line in place if the new line is shorter than the old one.
  You might be overwriting part of the next line if the new line is longer than the old line
• The code searches the 'C[]' array and not the file, is the array and file guaranteed to be in sync? Are you searching the array or the file?
• The line " for(int i = 0; i < count ; i++)" has a variable 'Count'. Where is 'Count' defined?