How to read past EOF from getc?

Question

I am writing a XOR encryption program which works fine during encryption but during decryption the

char ca2=fgetc(f);

gets stuck a

Answer 1

Your problem is right here:

f=fopen(filename,"r");

You open the file for text reading, not for binary. Your file size function gets it right, but your decoder function does not.

The idiomatic way to read a file character by character using the C-style IO routines is like this:

f = fopen(filename, "rb");

if (!f)
    // handle error

int c;   // NOTE:  int, not char!

while ( (c = fgetc(f)) != EOF )
{
    // do something with 'c'
}

This idiom does not require you to get the file size as a separate operation. You can rewrite your XOR "encryption" routine with a simple loop of the above form. It will be much clearer and more concise.

Your entire decoder function could be rewritten as follows: (minus the debug code)

int endec(char filename[], char psdw[])
{
     int inphash = inhash(psdw) % 50;
     char temp[999999];  // really, should be std::vector<char>
     FILE *f;

     if ( (f = fopen(filename, "rb")) == NULL )
     {
         printf("opening for read failed\n");
         return -1;
     }

     size_t crs = 0;
     int    c;

     while ( (c = fgetc(f)) != EOF )
     {
         inphash += 2;
         temp[crs++] = (char)(inphash ^ c);
     }
     fclose(f);

     if ( (f = fopen(filename, "wt")) == NULL )
     {
         printf("opening for write failed\n");
         return -1;
     }

     if (fwrite(temp, crs, 1, f) != crs)
     {
         printf("short write\n");
         fclose(f);
         return -1;
     }

     fclose(f);
     return 0;
 }

Not stellar error handling, but it is error handling.