Read a line from text file and delete it

Question

I want to read a text file line by line, perform some checks, and if the line is not required, delete it. I have done the code for reading line, but I don't know how to delete that line if it is not required by me. Please help me find the simplest method for deleting the line. Here is my code snippet what I tried:

   char ip[32];
   int port;
   DWORD dwWritten;
   FILE *fpOriginal, *fpOutput;
   HANDLE hFile,tempFile;
   hFile=CreateFile("Hell.txt",GENERIC_READ|GENERIC_WRITE,FILE_SHARE_READ|FILE_SHARE_WRITE,0,CREATE_ALWAYS,FILE_ATTRIBUTE_NORMAL,0);
   tempFile=CreateFile("temp.txt",GENERIC_READ|GENERIC_WRITE,FILE_SHARE_READ|FILE_SHARE_WRITE,0,CREATE_ALWAYS,FILE_ATTRIBUTE_NORMAL,0);
   WriteFile(hFile,"10.0.1.25 524192\r\n\r\n10.0.1.25 524193\r\n\r\n",strlen("10.0.1.25 524192\r\n\r\n10.0.1.25 524193\r\n\r\n"),&dwWritten,0);
   fpOriginal = fopen("Hell.txt", "r+");
   fpOutput = fopen("temp.txt", "w+");

   while (fscanf(fpOriginal, " %s %d", ip, &port) > 0) 
      {
         printf("\nLine1:");
         printf("ip: %s, port: %d", ip, port);
         char portbuff[32], space[]=" ";
         sprintf(portbuff, "%i",port);
         strcat(ip," ");
         strcat(ip,portbuff);
         if(port == 524192)
            printf("\n Delete this Line now");
         else
            WriteFile(tempFile,ip,strlen(ip),&dwWritten,0);
      }

     fclose(fpOriginal);
     fclose(fpOutput);
     CloseHandle(hFile);
     CloseHandle(tempFile);
     remove("Hell.txt");
     if(!(rename("temp.txt","Bye.txt")))
     {
         printf("\ncould not rename\n");
     }
     else 
        printf("\nRename Done\n");
     //remove ("Hell.txt");

Answer 1

You can copy all line wich does not contain the number 2 into a new file and then use the new file instead the old file

fp = fopen("File.txt", "r");
fp2 = fopen("File_copy.txt", "w");
while (fscanf(fp, " %s %d", string, &number) > 0) {
        if(number != 2)
        {
             fprintf(fp2, "%s %d\n", string, number);
        }
}
close(fp);
close(fp2);
remove("File.txt");
rename( "File_copy.txt", "File.txt" );

Answer 2

here's an example:

char* inFileName = "test.txt";
char* outFileName = "tmp.txt";
FILE* inFile = fopen(inFileName, "r");
FILE* outFile = fopen(outFileName, "w+");
char line [1024]; // maybe you have to user better value here
int lineCount = 0;

if( inFile == NULL )
{
    printf("Open Error");
}

while( fgets(line, sizeof(line), inFile) != NULL )
{
    if( ( lineCount % 2 ) != 0 )
    {
        fprintf(outFile, "%s", line);
    }

    lineCount++;
}


fclose(inFile);
fclose(outFile);

// possible you have to remove old file here before
if( !rename(inFileName, outFileName) )
{
    printf("Rename Error");
}

Answer 3

There are many to solve this problem one of them is, you can open another file for writing when you reach at a point where you don't want to write omit that paint and continue writing until end of file. Latterly you can delete old file and rename new file with old one.

if(number == 2)
{
     continue;
}
else
{
    writetofilefunction()
}

Answer 4

Another solution could be to write back to the same file (write back what you read out except for the lines you don't want) and use the Windows API function SetEndOfFile to truncate it when finished. This will probably be a bit messier to code but you won't need to create a second copy of the file so it's more efficient from a disk usage standpoint.