Q38730: Changing Default int to 32 Bits

Article: Q38730
Product(s): See article
Version(s): 4.00 5.00 5.10 | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): END-USER | SR# G881110-6126 | mspl13_c
Last Modified: 12-DEC-1988

Question:

I am porting a VERY large C program from another C compiler to OS/2.
In the other compiler, the type int is defined as being the same as
long (i.e., 32 bits). In Microsoft C, int is defined as being the same
as short (i.e., 16 bits).

Is there a compiler switch to change int to long rather than short?

Response:

There's no compiler switch that changes the default int to long rather
than short. If you included a "typedef long int;" or a "#define int
long" in each and every module you compiled, you would take care of
some of the problems. However, redefining the identifier "int" is
likely to cause you severe and difficult-to-find problems. We
emphatically do NOT recommend it.

Note: K & R and ANSI are both very clear that int could be any size,
provided that it's at least 16 bits. It is bad coding practice to rely
on 32-bit ints because it makes porting code difficult.

Changing all int variables to long causes your program to run very
slowly because whenever it does arithmetic, it will have to do slower
32-bit arithmetic rather than the more efficient built-in 16-bit
arithmetic. This situation is true even on 80386 processors because
current versions of our compilers do not support the generation of
code that takes advantage of the 80386's 32-bit registers.

A far better strategy is to change only the variables that need to be
long to long. This way, you will avoid a lot of unintended side
effects and you will not do more 32-bit arithmetic than is necessary.

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