Slide 14.6: Linking to C/C++ (cont.)

Linking to C/C++ (Cont.)

Code Example—Encrypting a File
The following program reads a file, encrypts it, and writes the output to another file. It includes three files:

main.cpp: The C++ startup program reads the names of the input and output files from the command line. It calls Encrypt from a loop that reads blocks of data from a file, encrypts it, and writes the translated buffer to a new file.

Encrypt.h: The header file contains a single function prototype:
```
   void Encrypt( char* buf, long count, char eChar );
```
Encrypt.asm: The Encrypt procedure loops through a character array and XOR each character with a predefined value.

To run this program from a command prompt, pass the names of the input and output files, for example,

   Encrypt  infile.txt outfile.txt

Some of the following C++ commands are used in the program:

bool eof( ) const;: The function returns true if the End-Of-File has been reached.

streamsize gcount( ) const;: Returns the number of bytes extracted by the last unformatted input operation performed on this object.

istream& read( char* s, streamsize n );: Reads a block of data of the length specified by n.

ostream& write( const char* str , streamsize n );: Inserts into the output stream a sequence of characters starting by character pointed by str and following by successive characters in the array until the number of characters specified by n has been successfully written.