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ceofgetc

Why can't use "getc(f)) != EOF" to compare directly?

I'm new to C language, and now get stuck with this kind of question: why do I get a weird result if I use above expression to print string in file?

Here is the situation: I have a file(data.txt) with the following content:

"Hello Everyone!!"

And here is my code:

int main()
{
   FILE *ptr = fopen("data.txt", "r");

   if (ptr != NULL)
   {
      while (getc(ptr) != EOF)    //print all contents in data.txt
         printf("%c", getc(ptr));
   }
   else
      printf("Open file failed.");

   return 0;
}

The execution result is:

"el vroe!"

If I assign getc(ptr) to variable first and do comparing, everything goes fine.

What's the difference between this two methods?

Solution

  • You extract first char in condition of while and then extract second char in printf. So you print only each second char in a loop.

    If you want, do something like:

    int c;

while ((c = getc(ptr)) != EOF) {
printf("%c", c);
}