4.6.1.1 Consistency Checks

Inconsistent use of variables, arguments, and functions is checked within files as well as across them. Generally speaking, the same checks are performed for prototype uses, declarations, and parameters as lint checks for old-style functions. If your program does not use function prototypes, lint checks the number and types of parameters in each call to a function more strictly than the compiler. lint also identifies mismatches of conversion specifications and arguments in [fs]printf() and [fs]scanf() control strings.

Examples:

• Within files, lint flags non-void functions that “fall off the bottom” without returning a value to the invoking function. In the past, programmers often indicated that a function was not meant to return a value by omitting the return type: fun() {}. That convention means nothing to the compiler, which regards fun() as having the return type int. Declare the function with the return type void to eliminate the problem.

• Across files, lint detects cases where a non-void function does not return a value, yet is used for its value in an expression—and the opposite problem, a function returning a value that is sometimes or always ignored in subsequent calls. When the value is always ignored, it may indicate an inefficiency in the function definition. When it is sometimes ignored, it’s probably bad style (typically, not testing for error conditions). If you need not check the return values of string functions like strcat(), strcpy(), and sprintf(), or output functions like printf() and putchar(), cast the offending calls to void.

• lint identifies variables or functions that are declared but not used or defined; used, but not defined; or defined, but not used. When lint is applied to some, but not all files of a collection to be loaded together, it produces error messages about functions and variables that are:

  • Declared in those files, but defined or used elsewhere

  • Used in those files, but defined elsewhere

  • Defined in those files, but used elsewhere

    Invoke the-x option to suppress the first complaint, -u to suppress the latter two.