How to copy all the lines from the file except the deleted one?

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C++

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

int main(){
  FILE *fp1, *fp2;
  char fname[50] = "fiile.csv", ch, toFind[50], str[200], saved[200];
  int delLine=1, count=1;
  fp1 = fopen(fname, "r");
  fp2 = fopen("new.csv", "w");
  char * line1 = NULL;

  printf("Enter your id card number: ");
  scanf("%s", toFind);

  while(fgets(str, 200, fp1)){
    line1 = strtok(str, "\n");
    strcpy(saved, line1);
    if(strstr(saved, toFind)){
      printf("%s\n", saved);
      exit(0);
    }
  }

  return 0;
}

What I have tried:

In this code, I am trying to delete a line that I will get through the ID card number. I became able to fetch that line but unable to delete it. I know that a temporary file is needed and by copying all the text except the deleted one I can do that. But the problem is that I am unable to copy all the lines except the deleted one like in this example
Example

C++

ch = getc(fp1);
//except the line to be deleted
if (temp != delete_line){
    putc(ch, fp2);
}

Here getc() is used but I am using fgets() just to find a specific line through the ID card number. I don't know if it's possible through getc() or is there any other way?

Posted 12-Sep-20 4:56am

ibilalkayy

Updated 12-Sep-20 9:10am

KarstenK

v2

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Dave Kreskowiak · Answer 1 · 2020-09-12T05:13:00

CSV files are just text file. There's nothing special about them.

You cannot "delete" a line in a text file. You have to load the text file into memory, one line at a time, and then write the file back to a new file, skipping the line you don't want written.

Excuse the crudity of my code. It's been over a decade since I've touched C/C++:

C

int main(){
  FILE *sourceFP, *destinationFP;
  char fname[50] = "file.csv";
  char idToFind[50];

  //char * line1 = NULL;
  char lineBuffer[4096];                    // 4K text buffer for storing a line

  sourceFP = fopen(fname, "r");
  destinationFP = fopen("new.csv", "w");


  printf("Enter your id card number: ");
  scanf("%s", idToFind);

  while( fgets(lineBuffer, 4096, sourceFP ) != NULL )
  {
    lineBuffer = strtok(lineBuffer, ",");         // Your delimiter character should NOT be "\n"
                                                  // COMMA Separated Values
    // strcpy(saved, line1);                      // Why? You don't need to copy the line!
    if( strstr(idToFind, lineBuffer) == NULL)
    {
      // The id was not found so write the line to the new file.
      printf("%s\n", lineBuffer);
      // exit(0);                                 // WHAT?! Write one line to the file then quit the app?
    }
  }

  return 0;
}

Rick York · Answer 2 · 2020-09-12T09:11:00

Try this code. It looks for exact match of card number and writes the data to the new file if it doesn't match. Buffer sizes have 1 added to allow for a terminating null and so you don't have to subtract one everywhere else you use the buffer.

C

#define BUFFER_LENGTH 199

int main()
{
  FILE *fp1, *fp2;
  char fname[50] = "fiile.csv", ch, toFind[50], str[BUFFER_LENGTH+1], saved[BUFFER_LENGTH+1];
  int count=0;
  fp1 = fopen(fname, "r");
  fp2 = fopen("new.csv", "w");
  char * line1 = NULL;

  printf("Enter your id card number: ");
  scanf("%s", toFind);

  while( fgets( str, BUFFER_LENGTH, fp1 ) )
  {
    ++count;
    strcpy( saved, str );     // save a copy because strtok is destructive
    line1 = strtok( str, "," );
    if( strcmp( line1, toFind ) == 0 )  // first token must match number exactly
    {
        printf( "line %d : %s\n", count, saved );   // found it, print it
//      exit(0);   // why?  have to write the rest of the file
    }
    else
    {
        fputs( saved, fp2 );   // not the one - write it to new file
    }
  }

  // close the files

  fclose( fp2 );
  fclose( fp1 );
  return 0;
}

How to copy all the lines from the file except the deleted one?

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