Slide 13.8: Calling C/C++ functions

Slide 13.7: Linking to C/C++ (cont.)
Slide 13.9: Calling C/C++ functions (cont.)
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Calling C/C++ Functions

You can write assembly language programs that call C++ functions. There are at least a couple of reasons for doing so:

Input-output is more flexible under C++, with its rich iostream library. For example,
- cin represents the standard input stream.
- cout represents the standard output stream.

C++ has extensive math libraries.

When calling functions from the standard C/C++ library, you must start the program from a C/C++ main( ) procedure to allow library initialization code to run.

Function Prototypes
C++ functions called from assembly language code must be defined with the "C" and extern keywords. Here is the basic syntax:

 
 
   extern  "C"  funName( paramlist ) {
 
 
      ...   }

Here is an example:

 
 
   extern  "C"  int  askForInteger( ) {
 
 
      cout << "Please enter an integer:";
 
 
      // ...
 
 
   }

Rather than modifying every function definition, it's easier to group multiple function prototypes inside a block. Then you can omit extern and "C" from the function implementations:

 
 
   extern  "C" {
 
 
      int  askForInteger( );
 
 
      int  showInt( int value, unsigned outWidth );
 
 
      etc.
 
 
   }

“I’m not arguing, I’m just explaining why I’m right.”
― Unknown