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

lint: C Program Checker XENIX Programming
It is difficult to detect when a function return is implied by the flow of control reaching
the end of the given function. This is demonstrated with a simple example:
f (a)
{
}
if (a)
g();
return (3);
Note that if the variable a tests false, f will call the function g and then return with no
defined return value. This will trigger a report from lint. If g, like exit, never returns,
the message will still be produced when in fact nothing is wrong. In practice,
potentially serious bugs can be discovered with this feature. It also accounts for a
substantial fraction of the noise messages produced by lint.
Checking for Unused Return Values
The lint program checks for cases where a function returns a value, but the value is
rarely if ever used. lint considers functions that return unused values to be inefficient
and functions that return rarely used values to be a result of bad programming style.
lint also checks for cases where a function does not return a value but the value is used
anyway. This is considered a serious error.
Checking Types
lint enforces the type checking rules of C more strictly than the C compiler. The
additional checking occurs in four major areas:
• Across certain binary operators and implied assignments
• At the structure selection operators
• Between the definit ion and uses of functions
• In the use of enumerations
A number of operators, including the assignment, conditional, and relational operators,
have an implied balancing between types of operands. The argument of a return
statement and expressions used in initialization also suffer similar conversions. In these
operations, char, short, int, long, unsigned, float, and double types can be freely
intermixed. The types of pointers must agree exactly, except that arrays of x's can be
intermixed with pointers to x's.
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