Intel XENIX 286 Programmers Guide (86) - Tenox.tc

cc: C Compiler XENIX Programming
Using Advanced Options
The cc command provides a nu mber of advanced programming options that give greater
control over the compilation process and the final form of the executable program. The
following sections describe a number of these options.
Using the near and far Keyword s
The near and far keywords are special type modifiers that define the length and meaning
of the address of a given variable. The near keyword defines an object with a 16-bit
address. The far keyword defines an object with a full 32-bit segmented address. Any
data item or function can be accessed.
The near and far keywords override the normal address length generated by the compiler
for variables and functions. In small model programs, far can be used to access data and
functions in segments outside of the program. In middle and large model programs, near
can be used to access data with just an offset.
The examples in Table 2-1 illustrate the far and near keywords as used in declarations in
a small model program.
*
**
***
2-16
Table 2-1. Examples of near and far Keywords in a Small Model Program
Declaration
char c;
char far d;
char *p;
char far *q;
char * far r;
char far * far s;
int foo();
int far foo();
Address Size
near (16 bits)
far (32 bits)
near (16 bits)
near (16 bits)
far (32 bits)
far (32 bits)
near (16 bits)
far (32 bits)
This is shown for syntactic completeness.
This is similar to accessing data in a long model program.
Item Size
8 bits (data)
8 bits (data)
16 bits (near pointer)
32 bits (far pointer)
16 bits (near pointer)*
32 bits (far pointer)**
function returning 16 bits
function returning 16 bits***
This example leads to trouble in most environments. The far call changes the CS
register and makes run time support unavailable.