C implementation of cp

Question

This is a primitive implementation of cp, i compiled and ran it on Linux machine(Ubuntu), this code works fine for text files of any size but not for pdfs or mp3, i dont know what im dong wrong. Is it wrong the way i use EOF? It compiles and runs without error, but does not work for every kind of file.

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

 #define MAX_SIZE 2
 #define MAX_BUF_SIZE 256

 int main(int argc, char* argv[])
 {
  FILE *pFile_src=NULL;
  FILE *pFile_dest=NULL;

  char* mychar;
  char *SRC, *DEST;
  int i=0,j;

  char char_buff[MAX_BUF_SIZE];
  mychar= (char *)malloc(sizeof(char *));

  if(argv[1]!=NULL)
      SRC=argv[1];
  else
      printf("\nUSAGE: ./Ex_ManualCP_prog src_file dest_file.\nFirst arg should be a filename, cannot be empty.\n");

  if(argv[2]!=NULL)
      DEST=argv[2];
  else
      printf("\nSecond arg should be a filename, cannot be empty.\n");

  mychar= (char *)malloc(MAX_SIZE*sizeof(char *));

  //initialize text buffer
  for(j=0;j<MAX_BUF_SIZE;j++)
      char_buff[j]='\0';

  pFile_src=fopen(SRC,"r");     //Open file to read and store in a character buffer

  pFile_dest=fopen(DEST,"w");  //open destination file

  if(pFile_dest==NULL)
      printf("\nFile specified as Destination DOES NOT EXIST.\n");

  if(pFile_src==NULL)
      printf("\nFile specified as Source, DOES NOT EXIST.\n");
  else
  {
   //printf("\n----File opened successfully-----\n");

       while(((*mychar=fgetc(pFile_src))!=EOF))
       {
             if(i>=MAX_BUF_SIZE)
             {
                i=0;
             }

             char_buff[i]=*mychar;
             fputc(char_buff[i],pFile_dest); //write buffer data into opened file
             ++i;
        }

       char_buff[i]='\0';
       fclose(pFile_src);  //close source file

   }

   fclose(pFile_dest);

   if(pFile_src!=NULL && pFile_dest!=NULL)
       printf("\n\n-----Copy Done!----\n-----Reached end of file.-----\n");

return 0;
}

Answer 1

Is it wrong the way i use EOF?

It is wrong. EOF is of type int. The return value of fgetc is also of type int. You store the value in a char.

Your code will fail if the file contains any byte with the value -1/255. Text files won't, of course, but large binary files are likely to contain such bytes.

Changing the type of mychar to int will fix that problem.

Another bug is the possible buffer overflow when you NUL-terminate char_buff. If the file is an even multiple of 256 then i will be 256 when you add the NUL-terminator and you will write outside the buffer.