// c.cpp
//
// Generic C++ driver program to demonstrate
// returning function results from assembly
// language to C++. Also includes a
// "readLine" function that reads a
// string from the user and passes it
// on to the assembly language code.
//
// Need to include stdio.h so this
// program can call "printf" and
// stdio.h so this program can call
// strlen.

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// extern "C" namespace prevents
// "name mangling" by the C++
// compiler.

extern "C"
{
    // asmMain is the assembly language
    // code's "main program":
        
    void asmMain( void );
    
    // getTitle returns a pointer to a
    // string of characters from the
    // assembly code that specifies the
    // title of that program (that makes
    // this program generic and usable
    // with a large number of sample
    // programs in "The Art of 64-bit
    // Assembly Language."
    
    char *getTitle( void );
    
    // C++ function that the assembly
    // language program can call:
    
    int readLine( char *dest, int maxLen );

};

// readLine reads a line of text from the
// user (from the console device) and stores
// that string into the destinatio buffer
// the first argument specifies. Strings
// are limited in length to the value specified
// by the second argument (minus 1).
// 
// This functionreturns the number of 
// characters actually read, or -1 if there 
// was an error.
//
// Note that if the user enters too many
// characters (maxlen or more) then this
// function only returns the first maxlen-1
// characters. This is not considered an
// error.

int readLine( char *dest, int maxLen )
{
    // Note: fgets returns NULL if there was
    // an error, else it returns a pointer to
    // the string data read (which will be the
    // value of the dest pointer).
	
    char *result = fgets( dest, maxLen, stdin );
	if( result != NULL )
	{
		// Wipe out the new line character at the
		// end of the string:
		
		int len = strlen( result );
		if( len > 0 )
		{
			dest[ len - 1 ] = 0;
		}
		return len;
	} 
    return -1; // If there was an error.
}

int main(void)
{
    // Get the assembly language program's title:
    
    char *title = getTitle();	
    
    printf( "Calling %s:\n", title );
    asmMain();
    printf( "%s terminated\n", title );
	
}