HP C Programmer's Guide (92434-90009)

124 Chapter5
Programming for Portability
Practices to Avoid
Practices to Avoid
To make a program portable, you need to minimize machine dependencies. The following
are programming practices you should avoid to ensure portability:
• Using dollar signs ($) in identifiers.
• Using underscores (_) as the first character in an identifier.
• Using sized enumerations.
• Reliance on implicit expression evaluation order.
• Making assumptions regarding storage allocation and layout.
• Dependence on the number of significant characters in an identifier. Identifiers should
differ as early as possible in the name. ANSI C requires that the first 31 characters of
an internal name are significant. Only the first 6 characters of an external name are
required to be significant by ANSI C.
• Dereferencing null pointers.
• Dependence on pointer representation.
• Dependence on being able to dereference a pointer to an object that is not correctly
aligned.
• Dependence on the ability to store a pointer in a variable of type int.
• Dependence on case distinctions in external names.
• Dependence on char being signed or unsigned.
• Dependence on bitwise operations in signed integers.
• Dependence on bit-fields of any type except int, unsigned int, or signed int.
• Dependence on the sign of the remainder in integer division.
• Dependence on right shifts of negative signed values.
• Dependence on more than six declarators modifying a basic type.
• Dependence on values of automatic variables after a longjmp call when the values were
changed between the setjmp and longjmp calls.
• Dependence on being able to call setjmp within an arbitrarily complex expression.
• Dependence on file system characteristics.
• Dependence on string literals being modifiable.
• Dependence on extern declarations within a block being visible outside of the block.