Sambar Server Documentation

CScript Function Definitions


Calling a function in CScript entails referencing its name with the appropriate arguments. The CScript interpreter checks for compatibility between the arguments in the calling sequence and the definition of the function. CScript assumes that every function will return a value. If the programmer wants a return value, this is achieved using the return statement. If no return value is required, none should be used when calling the function. Imporant! In C, the return type must be specified as part of the function definition. CScript does not require a return type be specified. In addition, in C, the types of the function arguments must be specified, these are optional in CScript as well. 

double power(double val, int pow)
{       
	double ret_val = 1.0;
        unsigned i;

        for (i = 0; i < pow; i++)
                ret_val *= val;

        return(ret_val);
}
The function follows a simple algorithm, multiplying the value by itself pow times. A for loop is used to control the number of multiplications, and variable ret_val stores the value to be returned.
double power(double val, double pow)
This line begins the function definition. It specifies the type of the return value, the name of the function, and a list of arguments used by the function. The arguments are enclosed in brackets and separated by commas. The body of the function is bounded by a set of curly brackets. Any variables declared here will be treated as local.
return(ret_val);
On reaching a return statement, control of the program returns to the calling function. The bracketed value is the value which is returned from the function. If the final closing curly bracket is reached before any return value, then the function will return automatically, any return value will then be meaningless.

Modifying Function Arguments

Some functions work by modifying the values of their arguments. This may be done to pass more than one value back to the calling routine, or because the return value is already being used in some way. CScript requires special arrangements for arguments whose values will be changed.

You can treat the arguments of a function as variables, however direct manipulation of these arguments won't change the values of the arguments from the calling function. The argument of the called function is just a copy of the calling value. This value is stored in a temporary variable which disappears on return from the function.

Direct changes to the argument variables are confined to the scope of that function. We can solve this problem by passing the addresses of variables to the function. These addresses, or pointers as they are generally known, behave a bit like integer types, except that a limited number of arithmetic operators can be applied to them.

To get back to our original function, we pass it the address of a variable whose value we wish to change. The function then uses the value at that address (or at the end of the pointer). On return from the function, the desired value will have changed. We manipulate the actual value using a copy of the pointer.

Important! The same syntax is used to pass variables by pointer so they can be manipulated by a function. However, in C, to manipulate the pointer location you must use a star (*) to reference the location of the variable in the function. In CScript, knowledge of the variable pointer location is implicit, so regular assignment can be performed.

C function
swap(a, b)
{
    c = *b;
    *b = *a;
    *a = c;
}

a = 1;
b = 2;
swap(&a, &b);
// Result: a == 2, b == 1   
 CScript function
swap(a, b)
{
    c = b; // pointer redirection is implicit
    b = a;
    a = c;
}

a = 1;
b = 2;
swap(&a, &b);
// Result: a == 2, b == 1

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