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Created page with "HI-TECH C eliminates many of the machine dependent aspects of C, since it uniformly implements such features as unsigned char. There are however certain areas where machi..."
HI-TECH C eliminates many of the machine dependent
aspects of C, since it uniformly implements such features as
unsigned char. There are however certain areas where machine
dependencies are inherent in the C language; programmers
should be aware of these and take them into account when
writing portable code.
The most obvious of these machine dependencies is the
varying size of C types; on some machines an int will be 16
bits, on others it may be 32 bits. HI-TECH C conforms to the
following rules, which represent common practice in most C
compilers.
char is at least 8 bits
short is at least 16 bits
long is at least 32 bits
int is the same as either short or long
float is at least 32 bits
double is at least as wide as float
Because of the variable width of an int, it is recom-
mended that short or long be used wherever possible in
preference to int. The exception to this is where a quantity
is required to correspond to the natural word size of the
machine.
Another area of machine differences is that of byte
ordering; the ordering of bytes in a short or long can vary
significantly between machines. There is no easy approach to
this problem other than to avoid code which depends on a
particular ordering. In particular you should avoid writing
out whole structures to a file (via _�f_�w_�r_�i_�t_�e()) unless the
file is only to be read by the same program then deleted.
Different compilers use different amounts of padding between
structure members, though this can be modified via the
#pragma pack(n) construct.
== Predefined Macros ==
One technique through which machine unavoidable machine
dependencies may be managed is the predefined macros pro-
vided by each compiler to identify the target processor and
operating system (if any). These are defined by the compiler
driver and may be tested with conditional compilation
preprocessor directives.
The macros defined by various compilers are listed in
table 2. These can be used as shown in the example in fig .
___________________________________________
|_M�_a�_c�_r�_o�_______________D�_e�_f�_i�_n�_e�_d�__f�_o�_r�_____________�|
| i8051 8051 processor family |
| i8086 8086 processor family |
| i8096 8096 processor family |
| z80 Z80 processor and derivatives |
| m68000 68000 processor family |
| m6800 6801, 68HC11 and 6301 processors|
| m6809 6809 processor |
| DOS MS-DOS and PC-DOS |
| CPM CP/M-80 and CP/M-86 |
| TOS Atari ST |
|___________________________________________�|
Table 2. Predefined Macros
#if DOS
char * filename = "c:file";
#endif /* DOS */
#if CPM
char * filename = "0:B:afile";
#endif /* CPM */
aspects of C, since it uniformly implements such features as
unsigned char. There are however certain areas where machine
dependencies are inherent in the C language; programmers
should be aware of these and take them into account when
writing portable code.
The most obvious of these machine dependencies is the
varying size of C types; on some machines an int will be 16
bits, on others it may be 32 bits. HI-TECH C conforms to the
following rules, which represent common practice in most C
compilers.
char is at least 8 bits
short is at least 16 bits
long is at least 32 bits
int is the same as either short or long
float is at least 32 bits
double is at least as wide as float
Because of the variable width of an int, it is recom-
mended that short or long be used wherever possible in
preference to int. The exception to this is where a quantity
is required to correspond to the natural word size of the
machine.
Another area of machine differences is that of byte
ordering; the ordering of bytes in a short or long can vary
significantly between machines. There is no easy approach to
this problem other than to avoid code which depends on a
particular ordering. In particular you should avoid writing
out whole structures to a file (via _�f_�w_�r_�i_�t_�e()) unless the
file is only to be read by the same program then deleted.
Different compilers use different amounts of padding between
structure members, though this can be modified via the
#pragma pack(n) construct.
== Predefined Macros ==
One technique through which machine unavoidable machine
dependencies may be managed is the predefined macros pro-
vided by each compiler to identify the target processor and
operating system (if any). These are defined by the compiler
driver and may be tested with conditional compilation
preprocessor directives.
The macros defined by various compilers are listed in
table 2. These can be used as shown in the example in fig .
___________________________________________
|_M�_a�_c�_r�_o�_______________D�_e�_f�_i�_n�_e�_d�__f�_o�_r�_____________�|
| i8051 8051 processor family |
| i8086 8086 processor family |
| i8096 8096 processor family |
| z80 Z80 processor and derivatives |
| m68000 68000 processor family |
| m6800 6801, 68HC11 and 6301 processors|
| m6809 6809 processor |
| DOS MS-DOS and PC-DOS |
| CPM CP/M-80 and CP/M-86 |
| TOS Atari ST |
|___________________________________________�|
Table 2. Predefined Macros
#if DOS
char * filename = "c:file";
#endif /* DOS */
#if CPM
char * filename = "0:B:afile";
#endif /* CPM */
