Programming in C Base 64 Decode File Write a program that accepts one command li

Question

Programming in C Base 64 Decode File

Write a program that accepts one command line argument, which is the name of a base-64
encoded text file.

The program is to base-64 decode the file, which is to be treated as a text file, outputting the
result into a second file (to be treated as a binary file) using as the name the string of text read
from the first line of the input file.

Your program should print to the console the total number of bytes written to the output file

base-64.c

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

char map(unsigned value)
{
   if (value < 26) return 'A' + value;
   if (value < 52) return 'a' + value - 26;
   if (value < 62) return '0' + value - 52;
   if (62 == value) return '+';
   if (63 == value) return '/';
      
   return '?';
}

unsigned unmap(char c)
{
   if ('/' == c)   return 63;
   if ('+' == c)   return 62;
   if (isdigit(c)) return 52 + (c - '0');
   if (islower(c)) return 26 + (c - 'a');
   if (isupper(c)) return 0 + (c - 'A');
      
  
   return 0xFFFFFFFF;
}

int main(void)
{
   char *message = "Hello World!";
  
   unsigned data = 062434752; // 0xCA35EA;
   char chars[4];
  
   printf("DATA: %o ", data);
  
   int i;
   for (i = 0; i < 4; i++)
   {
       unsigned value = (data >> (18 - 6 * i)) & 077;
      
       chars[i] = map(value);
   }
  
   printf("MSG : ");
   int i4;
   for (i4 = 0; i4 < 4; i4++)
   {
      
       printf("%c", chars[i4]);
   }
   printf(" ");
  
   data = 0;
   int i2;
   for (i2 = 0; i2 < 4; i2++)
   {
       unsigned value = unmap(chars[i2]);
      
       data <<= 6;
       data += value;
   }
  
   printf("DATA: %o ", data);

   return EXIT_SUCCESS;
}

Explanation / Answer

char *message = "Hello World!";
  
   unsigned data = 062434752; // 0xCA35EA;
   char chars[4];
  
   printf("DATA: %o ", data);
  
   int i;
   for (i = 0; i < 4; i++)
   {
       unsigned value = (data >> (18 - 6 * i)) & 077;
      
       chars[i] = map(value);
   }
  
   printf("MSG : ");
   int i4;
   for (i4 = 0; i4 < 4; i4++)
   {
      
       printf("%c", chars[i4]);
   }
   printf(" ");
  
   data = 0;
   int i2;
   for (i2 = 0; i2 < 4; i2++)
   {
       unsigned value = unmap(chars[i2]);
      
       data <<= 6;
       data += value;

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