Calling C/C++ Functions (Cont.)

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Function Return Values
The following list shows how Microsoft C++ functions return values:

• bool and char values are returned in AL.
• short int values are returned in AX.
• int and long int values are returned in EAX.
• Pointers are returned in EAX.
• float, double, and long double values are pushed on the floating-point stack as 4-, 8-, and 10-byte values, respectively.

Code Example—Finding all Factors
The following application prompts the user for an integer, finds all its factors, and displays each factor with leading padded spaces. The assembly language module will contain calls to two functions, for input-output, written in C++. The program will be launched from C++, main.cpp:

• The C++ function main( ) is the entry point of main.cpp. It ensures the execution of required C++ language initialization code.


• The assembly procedure DisplayFactors performs the following tasks:
  
  
  1. Calls askForInteger that inputs an integer n from the user.
  2. Uses a loop to repeatedly divide the input by the index from n to 1.
  3. Displays the divisor by calling showInt if the remainder is zero. ECX must be pushed and popped before calling showInt because Visual C++ functions may use general-purpose registers and do not save and restore them.


• The C++ function askForInteger( ) returns its result in the EAX register.


• The C++ function showInt displays an integer with a specified width by using setw.