NAME

lint — a C program verifier

SYNOPSIS

lint [-abceghprvwxzHFV] [-s | -t] [-i | -nu] [-D name[=def]] [-U name] [-I directory] [-d directory] [-L directory] [-MD] [-l library] [-o outputfile] [-B directory] [-X id[,id ...]] file ...

lint [-abceghprvwzHFV] [-s | -t] -C library [-D name[=def]] [-U name] [-I directory] [-d directory] [-B directory] [-X id[,id ...]] file ...

DESCRIPTION

The lint utility attempts to detect features of the named C program files that are likely to be bugs, to be non-portable, or to be wasteful. It also performs stricter type checking than does the C compiler. The lint utility runs the C preprocessor as its first phase, with the preprocessor symbol “lint” defined to allow certain questionable code to be altered or skipped by lint. Therefore, this symbol should be thought of as a reserved word for all code that is to be checked by lint.

Among the possible problems that are currently noted are unreachable statements, loops not entered at the top, variables declared and not used, and logical expressions with constant values. Function calls are checked for inconsistencies, such as calls to functions that return values in some places and not in others, functions called with varying numbers of arguments, function calls that pass arguments of a type other than the type the function expects to receive, functions whose values are not used, and calls to functions not returning values that use the non-existent return value of the function.

Filename arguments ending with .c are taken to be C source files. Filename arguments with names ending with .ln are taken to be the result of an earlier invocation of lint, with either the -i, -o, or -C option in effect. The .ln files are analogous to the .o (object) files produced by cc(1) from .c files. The lint utility also accepts special libraries specified with the -l option, which contain definitions of library routines and variables.

The lint utility takes all the .c, .ln, and llib-llibrary.ln (lint library) files and processes them in command-line order. By default, lint appends the standard C lint library (llib-lc.ln) to the end of the list of files. When the -i option is used, the .ln files are ignored. Also, when the -o or -i options are used, the llib-llibrary.ln files are ignored. When the -i option is omitted the second pass of lint checks this list of files for mutual compatibility. At this point, if a complaint stems not from a given source file, but from one of its included files, the source filename will be printed followed by a question mark.

The special input file name “-” causes lint to take input from standard input (until end of file) and process it as if it were a .c file. If the -i flag is given and “-” is named as one of the input files, the -o flag must also be specified to provide an output file name. The options are as follows:

-a: Report assignments of long values to variables that are not long.
-aa: Additional to -a, report all assignments of integer values to other integer values which cause implicit narrowing conversion.
-b: Report break statements that cannot be reached. This is not the default because, unfortunately, most lex(1) and many yacc(1) outputs produce many such complaints.
-c: Complain about casts which have questionable portability.
-e: Complain about unusual operations on enum-Types and combinations of enum- and integer-Types.
-g: Do not print warnings for some extensions of gcc(1) to the C language. Currently these are nonconstant initializers in automatic aggregate initializations, arithmetic on pointer to void, trailing commas in enum declarations, C++ -style “//” comments, zero sized structures, subscripting of non-lvalue arrays, prototypes overriding old style function declarations and long long integer types. The -g flag also turns on the keywords asm and inline (alternative keywords with leading underscores for both asm and inline are always available).
-h: Apply a number of heuristic tests to attempt to intuit bugs, improve style, and reduce waste.
-i: Produce a .ln file for every .c file on the command line. These .ln files are the product of lint's first pass only, and are not checked for compatibility between functions.
-n: Do not check compatibility against the standard library.
-p: Attempt to check portability of code to other dialects of C.
-r: In case of redeclarations report the position of the previous declaration.
-s: Strict ANSI C mode. Issue warnings and errors required by ANSI C. Also do not produce warnings for constructs which behave differently in traditional C and ANSI C. With the -s flag, __STRICT_ANSI__ is a predefined preprocessor macro.
-S: C9X mode. Currently not fully implemented.
-t: Traditional C mode. __STDC__ is not predefined in this mode. Warnings are printed for constructs not allowed in traditional C. Warnings for constructs which behave differently in traditional C and ANSI C are suppressed. Preprocessor macros describing the machine type (e.g., sun3) and machine architecture (e.g., m68k) are defined without leading and trailing underscores. The keywords const, volatile and signed are not available in traditional C mode (although the alternative keywords with leading underscores still are).
-u: Do not complain about functions and external variables used and not defined, or defined and not used (this is suitable for running lint on a subset of files comprising part of a larger program).
-v: Suppress complaints about unused arguments in functions.
-x: Report variables referred to by extern declarations, but never used.
-z: Do not complain about structures that are never defined (for example, using a structure pointer without knowing its contents).
-B path: Path to use when looking for the lint1 and lint2 binaries. Defaults to /usr/libexec.
-C library: Create a lint library with the name llib-llibrary.ln. This library is built from all .c and .ln input files. After all global definitions of functions and variables in these files are written to the newly created library, lint checks all input files, including libraries specified with the -l option, for mutual compatibility.
-D name[=def]: Define name for cpp(1), as if by a #define directive. If no definition is given, name is defined as 1.
-I directory: Add directory to the list of directories in which to search for include files.
-d directory: Use directory instead of /usr/include as the default place to find include files.
-l library: Include the lint library llib-llibrary.ln.
-L directory: Search for lint libraries in directory and directory/lint before searching the standard place.
-F: Print pathnames of files. The lint utility normally prints the filename without the path.
-H: If a complaint stems from an included file lint prints the name of the included file instead of the source file name followed by a question mark.
-MD: Pass -MD to cpp(1) causing cpp to create files containing dependency information for each source file.
-o outputfile: Name the output file outputfile. The output file produced is the input that is given to lint's second pass. The -o option simply saves this file in the named output file. If the -i option is also used the files are not checked for compatibility. To produce a llib-llibrary.ln without extraneous messages, use of the -u option is suggested. The -v option is useful if the source file(s) for the lint library are just external interfaces.
-U name: Remove any initial definition of name for the preprocessor.
-V: Print the command lines constructed by the controller program to run the C preprocessor and lint's first and second pass.
-w: Treat warnings as errors.
-X id[,id ...]: Suppress error messages identified by the list of ids. A list of messages and ids can be found in lint(7).

Input Grammar

lint's first pass reads standard C source files. The lint utility recognizes the following C comments as commands.

/* ARGSUSEDn */: Makes lint check only the first n arguments for usage; a missing n is taken to be 0 (this option acts like the -v option for the next function).
/* BITFIELDTYPE */: Suppress error messages about illegal bitfield types if the type is an integer type, and suppress non-portable bitfield type warnings.
/* CONSTCOND */ or /* CONSTANTCOND */ or /* CONSTANTCONDITION */: suppress complaints about constant operands for the next expression.
/* FALLTHRU */ or /* FALLTHROUGH */: suppress complaints about fall through to a case or default labelled statement. This directive should be placed immediately preceding the label.
/* LINTLIBRARY */: At the beginning of a file, mark all functions and variables defined in this file as used. Also shut off complaints about unused function arguments.
/* LINTED [comment] */ or /* NOSTRICT [comment] */: Suppresses any intra-file warning except those dealing with unused variables or functions. This directive should be placed on the line immediately preceding where the lint warning occurred.
/* LONGLONG */: Suppress complaints about use of long long integer types.
/* NOTREACHED */: At appropriate points, inhibit complaints about unreachable code. (This comment is typically placed just after calls to functions like exit(3)).
/* PRINTFLIKEn */: makes lint check the first (n-1) arguments as usual. The n-th argument is interpreted as a printf(3) format string that is used to check the remaining arguments.
/* PROTOLIBn */: causes lint to treat function declaration prototypes as function definitions if n is non-zero. This directive can only be used in conjunction with the /* LINTLIBRARY */ directive. If n is zero, function prototypes will be treated normally.
/* SCANFLIKEn */: makes lint check the first (n-1) arguments as usual. The n-th argument is interpreted as a scanf(3) format string that is used to check the remaining arguments.
/* VARARGSn */: Suppress the usual checking for variable numbers of arguments in the following function declaration. The data types of the first n arguments are checked; a missing n is taken to be 0.

The behavior of the -i and the -o options allows for incremental use of lint on a set of C source files. Generally, one invokes lint once for each source file with the -i option. Each of these invocations produces a .ln file that corresponds to the .c file, and prints all messages that are about just that source file. After all the source files have been separately run through lint, it is invoked once more (without the -i option), listing all the .ln files with the needed -l library options. This will print all the inter-file inconsistencies. This scheme works well with make(1); it allows make(1) to be used to lint only the source files that have been modified since the last time the set of source files were linted.

ENVIRONMENT

LIBDIR: the directory where the lint libraries specified by the -l library option must exist. If this environment variable is undefined, then the default path /usr/libdata/lint will be used to search for the libraries.
TMPDIR: usually the path for temporary files can be redefined by setting this environment variable.
CC: Location of the C compiler program. Defaults to /usr/bin/cc.

FILES

/usr/libexec/lint[12]: programs
/usr/libdata/lint/llib-l*.ln: various prebuilt lint libraries
/tmp/lint*: temporaries

AUTHORS

Jochen Pohl

BUGS

The routines exit(3), longjmp(3) and other functions that do not return are not understood; this causes various incorrect diagnostics.
Static functions which are used only before their first extern declaration are reported as unused.
Libraries created by the -o option will, when used in later lint runs, cause certain errors that were reported when the libraries were created to be reported again, and cause line numbers and file names from the original source used to create those libraries to be reported in error messages. For these reasons, it is recommended to use the -C option to create lint libraries.