CODEWITHSUNDEEP
c
Peng Ren
Peng Ren

Reputation: 239

how to stop reading from binary file in c

I'm trying to use raw I/O functions to read from a file and output the data to another file however, it seems that my code cannot work, which I figured out is that the read() cannot be terminated. However, I don't know how to terminate the loop in the case, my code is like this:

int main(){
   int infile; //input file
   int outfile; //output file

   infile = open("1.txt", O_RDONLY, S_IRUSR);
   if(infile == -1){
      return 1; //error
   }
   outfile = open("2.txt", O_CREAT | ORDWR, S_IRUSR | S_IWUSR);
   if(outfile == -1){
      return 1; //error
   }

   int intch; //character raed from input file
   unsigned char ch; //char to a byte

   while(intch != EOF){ //it seems that the loop cannot terminate, my opinion
      read(infile, &intch, sizeof(unsigned char));
      ch = (unsigned char) intch; //Convert
      write(outfile, &ch, sizeof(unsigned char));
  }
   close(infile);
   close(outfile);

   return 0; //success
}

could somebody helps me on the problem? THank you a lot

Upvotes: 1

Views: 617

Answers (2)

thisisdog
thisisdog

Reputation: 948

intch is uninitialized 4 (or sometimes 8) bytes. You are only loading 1 byte into intch, and leaving the remaining bytes uninitialized. You then compare EOF with all of intch, which has not been fully initialized.

Try declaring intch as a char.

Upvotes: 0

Zeta
Zeta

Reputation: 105895

read will return 0 if you encounter the end of file:

while(read(infile, &intch, sizeof(unsigned char) > 0){ 
    ch = (unsigned char) intch; //Convert
    write(outfile, &ch, sizeof(unsigned char));
}

Note that a negative value indicates an error, so you might want to save the return of read.

Upvotes: 1

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