appending text to existing text file

[kpax]

Hi team,
This is doing my head in...and I'm sure i'm SO close to solving this! I need some guided help on how I can modify my code below, so that I can append some additional text to the beginning of a text file, which already has content within it.

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

int main(void)
{
  char str[80] = "This is just some random text.\n";
  FILE *fp;
  char *p;
  int i;

  /* open file3.txt for output */
  if((fp = fopen("file3.txt", "w"))==NULL) {
    printf("Cannot open file.\n");
    exit(1);
  }

  /* write str to disk */
  p = str;
  while(*p) {
    if(fputc(*p, fp)==EOF) {
      printf("Error writing file.\n");
      exit(1);
    }
    p++;
  }
  fclose(fp);

  /* open file3.txt for input */
  if((fp = fopen("file3.txt", "r"))==NULL) {
    printf("Cannot open file.\n");
    exit(1);
  }

  /* read back the file */
  for(;;) {
     i = fgetc(fp);
     if(i == EOF) break;
     putchar(i);
  }
  fclose(fp);

  return 0;
}

Basically, what this overwrites the contents of the file and just adds "This is just some random text."...

Would REALLY welcome any of you to show me the proper code!

Cheers,
K

[39ster]

According to http://www.cplusplus.com/reference/c...dio/fopen.html you need to use the mode "a" to append to the file.

EDIT: U want to add to front. sorry. read the reply below me

[Dino]

To add text to the front, you have two options:

1) Write to a new file, add the new text, and then copy all the text from the source file to the new file and when done, delete the original source file and rename the new file to the old name.

2) Open the file for read and write, read the whole file into memory, reset the file position to zero, and then write your new data followed by all the data you read into memory.

So, therefore, you are not so close.

[kpax]

thanks guys for your quick reply!
back to the drawing board I go.

Todd/39ster - do you have any references to how to do the above mentioned?

Cheers,

[Elysia]

kpax, I think it would be a very trivial task to open one file, read, then write into another file and repeat until you've finished writing the entire contents.
Try doing that and I'm sure you can finish your code.

[Dino]

Which one are you wanting to do? Have you learned about allocating memory yet?

[kpax]

thanks Elysia.

Nope haven't got to that stage about memory allocation.

I understand exactly what I need to do - the hard parts actually coding it

[Dino]

It's only hard when you let the whole scope of the effort overwhelm you.

Divide and conquer.

[matsp]

thanks Elysia.

Nope haven't got to that stage about memory allocation.

I understand exactly what I need to do - the hard parts actually coding it

And you will not learn how to do it if you don't do it yourself - just like you can't learn how to drive a car by watching someone drive on telly.

--
Mats