C Checker Reference Manual

January 1998

next section previous section current document TenDRA home page document index

6.1 - Introduction
6.2 - Preprocessor directives
6.3 - Indented Preprocessing Directives
6.4 - Multiple macro definitions
6.5 - Macro arguments
6.6 - Unmatched quotes
6.7 - Include depth
6.8 - Text after #endif
6.9 - Text after #
6.10 - New line at end of file

6 Preprocessing checks

6.1 Introduction

This chapter describes tchk's capabilities for checking the preprocessing constructs that arise in C.

6.2 Preprocessor directives

By default, the TenDRA C checker understands those preprocessor directives specified by the ISO C standard, section 6.8, i.e. #if, #ifdef, #ifndef, #elif, #else, #endif, #error, #line and #pragma. As has been mentioned, #pragma statements play a significant role in the checker. While any recognised #pragma statements are processed, all unknown pragma statements are ignored by default. The check to detect unknown pragma statements is controlled by:

	#pragma TenDRA unknown pragma permit
The option for permit are disallow (raise an error if an unknown pragma is encountered), warning (allow unknown pragmas with a warning), or allow (allow unknown pragmas without comment).

In addition, the common non-ISO preprocessor directives, #file, #ident, #assert, #unassert and #weak may be permitted using:

	#pragma TenDRA directive dir allow
where dir is the appropriate one of file, ident , assert, unassert or weak. If allow is replaced by warning then the directive is allowed, but a warning is issued. In either case, the modifier (ignore) may be added to indicate that, although the directive is allowed, its effect is ignored. Thus for example:

	#pragma TenDRA directive ident (ignore) allow
causes the checker to ignore any #ident directives without raising any errors.

Finally, the directive dir can be disallowed using:

	#pragma TenDRA directive dir disallow
Any other unknown preprocessing directives cause the checker to raise an error in the default mode. The pragma may be used to force the checker to ignore such directives without raising any errors.

	#pragma TenDRA unknown directive allow
Disallow and warning variants are also available.

6.3 Indented Preprocessing Directives

The ISO C standard allows white space to occur before the # in a preprocessing directive, and between the # and the directive name. Many older preprocessors have problems with such directives. The checker's treatment of such directives can be set using:

	#pragma TenDRA indented # directive permit
which detects white space before the # and:

	#pragma TenDRA indented directive after # permit
which detects white space between the # and the directive name. The options for permit are allow, warning or disallow as usual. The default checking profile allows both forms of indented directives.

6.4 Multiple macro definitions

The ISO C standard states that, for two definitions of a function-like macro to be equal, both the spelling of the parameters and the macro definition must be equal. Thus, for example, in:

	#define f( x ) ( x )
	#define f( y ) ( y )
the two definitions of f are not equal, despite the fact that they are clearly equivalent. Tchk has an alternative definition of macro equality which allows for consistent substitution of parameter names. The type of macro equality used is controlled by:

	#pragma TenDRA weak macro equality allow
where permit is allow (use alternative definition of macro equality),warning (as for allow but raise a warning), or disallow (use the ISO C definition of macro equality - this is the default setting).

More generally, the pragma: 

	#pragma TenDRA extra macro definition allow
allows macros to be redefined, both consistently and inconsistently. If the definitions are incompatible, the first definition is overwritten. This pragma has a disallow variant, which resets the check to its default mode.

6.5 Macro arguments

According to the ISO C standard, section 6.8.3, if a macro argument contains a sequence of preprocessing tokens that would otherwise act as a preprocessing directive, the behaviour is undefined. Tchk allows preprocessing directives in macro arguments by default. The check to detect such macro arguments is controlled by:

	#pragma TenDRA directive as macro argument permit
where permit is allow, warning or disallow.

The ISO C standard, section 6.8.3.2, also states that each # preprocessing token in the replacement list for a function-like macro shall be followed by a parameter as the next preprocessing token in the replacement list. By default, if tchk encounters a # in a function-like macro replacement list which is not followed by a parameter of the macro an error is raised. The checker's behaviour in this situation is controlled by: 

	#pragma TenDRA no ident after # permit
where the options for permit are allow (do not raise errors), disallow (default mode) and warning (raise warnings instead of errors).

6.6 Unmatched quotes

The ISO C standard, section 6.1, states that if a ` or " character matches the category of preprocessing tokens described as "single non-whitespace-characters that do not lexically match the other preprocessing token categories", then the behaviour is undefined. For example:

	#define a `b
would result in undefined behaviour. By default the ` character is ignored by tchk. A check to detect such statements may be controlled by:

	#pragma TenDRA unmatched quote permit
The usual allow, warning and disallow options are available.

6.7 Include depth

Most preprocessors set a maximum depth for #include directives (which may be limited by the maximum number of files which can be open on the host system). By default, the checker supports a depth equal to this maximum number. However, a smaller maximum depth can be set using:

	#pragma TenDRA includes depth n
where n can be any positive integral constant.

6.8 Text after #endif

The ISO C standard, section 6.8, specifies that #endif and #else preprocessor directives do not take any arguments, but should be followed by a newline. In the default checking mode, tchk raises an error when #endif or #else statements are not directly followed by a new line. This behaviour may be modified using:

	#pragma TenDRA text after directive permit
where permit is allow (no errors are raised and any text on the same line as the #endif or #else statement is ignored), warning or disallow.

6.9 Text after #

The ISO C standard specifies that a # occuring outside of a macro replacement list must be followed by a new line or by a preprocessing directive and this is enforced by the checker in default mode . The check is controlled by:

	#pragma TenDRA no directive/nline after ident permit
where permit may be allow, disallow or warning.

6.10 New line at end of file

The ISO C standard, section 5.1.1.2, states that source files must end with new lines. Files which do not end in new lines are flagged as errors by the checker in default mode. The behaviour can be modified using:

	#pragma TenDRA no nline after file end permit
where permit has the usual allow, disallow and warning options.

Part of the TenDRA Web.
Crown Copyright © 1998.