Appendix A Summary of guidelines


Rule 1.1 Required
The program shall contain no violations of the standard C syntax and constraints, and shall not exceed the implementation’s translation limits

Rule 1.2 Advisory
Language extensions should not be used

Rule 1.3 Required
There shall be no occurrence of undefined or critical unspecified behaviour

Rule 2.1 Required
A project shall not contain unreachable code

Rule 2.2 Required
There shall be no dead code

Rule 2.3 Advisory
A project should not contain unused type declarations

Rule 2.4 Advisory
A project should not contain unused tag declarations

Rule 2.5 Advisory
A project should not contain unused macro declarations

Rule 2.6 Advisory
A function should not contain unused label declarations

Rule 2.7 Advisory
There should be no unused parameters in functions

Rule 3.1 Required
The character sequences /* and // shall not be used within a comment

Rule 3.2 Required
Line-splicing shall not be used in // comments

Rule 4.1 Required
Octal and hexadecimal escape sequences shall be terminated

Rule 4.2 Advisory
Trigraphs should not be used

Dir 4.3 Required
Assembly language shall be encapsulated and isolated

Dir 4.4 Advisory
Sections of code should not be “commented out”

Dir 4.5 Advisory
Identifiers in the same name space with overlapping visibility should be typographically unambiguous

Dir 4.6 Advisory
typedefs that indicate size and signedness should be used in place of the basic numerical types

Dir 4.7 Required
If a function returns error information, then that error information shall be tested

Dir 4.8 Advisory
If a pointer to a structure or union is never dereferenced within a translation unit, then the implementation of the object should be hidden

Dir 4.9 Advisory
A function should be used in preference to a function-like macro where they are interchangeable

Dir 4.10 Required
Precautions shall be taken in order to prevent the contents of a header file being included more than once

Dir 4.11 Required
The validity of values passed to library functions shall be checked

Dir 4.12 Required
Dynamic memory allocation shall not be used

Dir 4.13 Advisory
Functions which are designed to provide operations on a resource should be called in an appropriate sequence

Rule 5.1 Required
External identifiers shall be distinct

Rule 5.2 Required
Identifiers declared in the same scope and name space shall be distinct

Rule 5.3 Required
An identifier declared in an inner scope shall not hide an identifier declared in an outer scope

Rule 5.4 Required
Macro identifiers shall be distinct

Rule 5.5 Required
Identifiers shall be distinct from macro names

Rule 5.6 Required
A typedef name shall be a unique identifier

Rule 5.7 Required
A tag name shall be a unique identifier

Rule 5.8 Required
Identifiers that define objects or functions with external linkage shall be unique

Rule 5.9 Advisory
Identifiers that define objects or functions with internal linkage should be unique

Rule 6.1 Required
Bit-fields shall only be declared with an appropriate type

Rule 6.2 Required
Single-bit named bit fields shall not be of a signed type

Rule 7.1 Required
Octal constants shall not be used

Rule 7.2 Required
A “u” or “U” suﬃx shall be applied to all integer constants that are represented in an unsigned type

Rule 7.3 Required
The lowercase character “l” shall not be used in a literal suﬃx

Rule 7.4 Required
A string literal shall not be assigned to an object unless the object’s type is “pointer to const-qualified char”

Rule 8.1 Required
Types shall be explicitly specified

Rule 8.2 Required
Function types shall be in prototype form with named parameters

Rule 8.3 Required
All declarations of an object or function shall use the same names and type qualifiers

Rule 8.4 Required
A compatible declaration shall be visible when an object or function with external linkage is defined

Rule 8.5 Required
An external object or function shall be declared once in one and only one file

Rule 8.6 Required
An identifier with external linkage shall have exactly one external definition

Rule 8.7 Advisory
Functions and objects should not be defined with external linkage if they are referenced in only one translation unit

Rule 8.8 Required
The static storage class specifier shall be used in all declarations of objects and functions that have internal linkage

Rule 8.9 Advisory
An object should be defined at block scope if its identifier only appears in a single function

Rule 8.10 Required
An inline function shall be declared with the static storage class

Rule 8.11 Advisory
When an array with external linkage is declared, its size should be explicitly specified

Rule 8.13 Advisory
A pointer should point to a const-qualified type whenever possible

Rule 8.14 Required
The restrict type qualifier shall not be used

Rule 9.1 Mandatory
The value of an object with automatic storage duration shall not be read before it has been set

Rule 9.2 Required
The initializer for an aggregate or union shall be enclosed in braces

Rule 9.3 Required
Arrays shall not be partially initialized

Rule 9.4 Required
An element of an object shall not be initialized more than once

Rule 9.5 Required
Where designated initializers are used to initialize an array object the size of the array shall be specified explicitly

Rule 10.1 Required
Operands shall not be of an inappropriate essential type

Rule 10.2 Required
Expressions of essentially character type shall not be used inappropriately in addition and subtraction operations

Rule 10.3 Required
The value of an expression shall not be assigned to an object with a narrower essential type or of a diﬀerent essential type category

Rule 10.4 Required
Both operands of an operator in which the usual arithmetic conversions are performed shall have the same essential type category

Rule 10.5 Advisory
The value of an expression should not be cast to an inappropriate essential type

Rule 10.6 Required
The value of a composite expression shall not be assigned to an object with wider essential type

Rule 10.7 Required
If a composite expression is used as one operand of an operator in which the usual arithmetic conversions are performed then the other operand shall not have wider essential type

Rule 10.8 Required
The value of a composite expression shall not be cast to a diﬀerent essential type category or a wider essential type

Rule 11.1 Required
Conversions shall not be performed between a pointer to a function and any other type

Rule 11.2 Required
Conversions shall not be performed between a pointer to an incomplete type and any other type

Rule 11.3 Required
A cast shall not be performed between a pointer to object type and a pointer to a diﬀerent object type

Rule 11.4 Advisory
A conversion should not be performed between a pointer to object and an integer type

Rule 11.5 Advisory
A conversion should not be performed from pointer to void into pointer to object

Rule 11.6 Required
A cast shall not be performed between pointer to void and an arithmetic type

Rule 11.7 Required
A cast shall not be performed between pointer to object and a noninteger arithmetic type

Rule 11.8 Required
A cast shall not remove any const or volatile qualification from the type pointed to by a pointer

Rule 11.9 Required
The macro NULL shall be the only permitted form of integer null pointer constant

Rule 12.1 Advisory
The precedence of operators within expressions should be made explicit

Rule 12.2 Required
The right hand operand of a shift operator shall lie in the range zero to one less than the width in bits of the essential type of the left hand operand

Rule 12.3 Advisory
The comma operator should not be used

Rule 12.4 Advisory
Evaluation of constant expressions should not lead to unsigned integer wrap-around

Rule 13.1 Required
Initializer lists shall not contain persistent side eﬀects

Rule 13.2 Required
The value of an expression and its persistent side eﬀects shall be the same under all permitted evaluation orders

Rule 13.3 Advisory
A full expression containing an increment (++) or decrement (--) operator should have no other potential side eﬀects other than that caused by the increment or decrement operator

Rule 13.4 Advisory
The result of an assignment operator should not be used

Rule 13.5 Required
The right hand operand of a logical && or || operator shall not contain persistent side eﬀects

Rule 13.6 Mandatory
The operand of the sizeof operator shall not contain any expression which has potential side eﬀects

Rule 14.1 Required
A loop counter shall not have essentially floating type

Rule 14.2 Required
A for loop shall be well-formed

Rule 14.3 Required
Controlling expressions shall not be invariant

Rule 14.4 Required
The controlling expression of an if statement and the controlling expression of an iteration-statement shall have essentially Boolean type

Rule 15.1 Advisory
The goto statement should not be used

Rule 15.2 Required
The goto statement shall jump to a label declared later in the same function

Rule 15.3 Required
Any label referenced by a goto statement shall be declared in the same block, or in any block enclosing the goto statement

Rule 15.4 Advisory
There should be no more than one break or goto statement used to terminate any iteration statement

Rule 15.5 Advisory
A function should have a single point of exit at the end

Rule 15.6 Required
The body of an iteration-statement or a selection-statement shall be a compound-statement

Rule 15.7 Required
All if … else if constructs shall be terminated with an else statement

Rule 16.1 Required
All switch statements shall be well-formed

Rule 16.2 Required
A switch label shall only be used when the most closely-enclosing compound statement is the body of a switch statement

Rule 16.3 Required
An unconditional break statement shall terminate every switch-clause

Rule 16.4 Required
Every switch statement shall have a default label

Rule 16.5 Required
A default label shall appear as either the first or the last switch label of a switch statement

Rule 16.6 Required
Every switch statement shall have at least two switch-clauses

Rule 16.7 Required
A switch-expression shall not have essentially Boolean type

Rule 17.1 Required
The features of <stdarg.h> shall not be used

Rule 17.2 Required
Functions shall not call themselves, either directly or indirectly

Rule 17.3 Mandatory
A function shall not be declared implicitly

Rule 17.4 Mandatory
All exit paths from a function with non-void return type shall have an explicit return statement with an expression

Rule 17.5 Advisory
The function argument corresponding to a parameter declared to have an array type shall have an appropriate number of elements

Rule 17.6 Mandatory
The declaration of an array parameter shall not contain the static keyword between the [ ]

Rule 17.7 Required
The value returned by a function having non-void return type shall be used

Rule 17.8 Advisory
A function parameter should not be modified

Rule 18.1 Required
A pointer resulting from arithmetic on a pointer operand shall address an element of the same array as that pointer operand

Rule 18.2 Required
Subtraction between pointers shall only be applied to pointers that address elements of the same array

Rule 18.3 Required
The relational operators >, >=, < and <= shall not be applied to objects of pointer type except where they point into the same object

Rule 18.4 Advisory
The +, -, += and -= operators should not be applied to an expression of pointer type

Rule 18.5 Advisory
Declarations should contain no more than two levels of pointer nesting

Rule 18.6 Required
The address of an object with automatic storage shall not be copied to another object that persists after the first object has ceased to exist

Rule 18.7 Required
Flexible array members shall not be declared

Rule 18.8 Required
Variable-length array types shall not be used

Rule 19.1 Mandatory
An object shall not be assigned or copied to an overlapping object

Rule 19.2 Advisory
The union keyword should not be used

Rule 20.1 Advisory
#include directives should only be preceded by preprocessor directives or comments

Rule 20.2 Required
The ', " or \ characters and the /* or // character sequences shall not occur in a header file name

Rule 20.3 Required
The #include directive shall be followed by either a <filename> or "filename" sequence

Rule 20.4 Required
A macro shall not be defined with the same name as a keyword

Rule 20.5 Advisory
#undef should not be used

Rule 20.7 Required
Expressions resulting from the expansion of macro parameters shall be enclosed in parentheses

Rule 20.8 Required
The controlling expression of a #if or #elif preprocessing directive shall evaluate to 0 or 1

Rule 20.9 Required
All identifiers used in the controlling expression of #if or #elif preprocessing directives shall be #define’d before evaluation

Rule 20.10 Advisory
The # and ## preprocessor operators should not be used

Rule 20.11 Required
A macro parameter immediately following a # operator shall not immediately be followed by a ## operator

Rule 20.12 Required
A macro parameter used as an operand to the # or ## operators, which is itself subject to further macro replacement, shall only be used as an operand to these operators

Rule 20.13 Required
A line whose first token is # shall be a valid preprocessing directive

Rule 20.14 Required
All #else, #elif and #endif preprocessor directives shall reside in the same file as the #if, #ifdef or #ifndef directive to which they are related

Rule 21.1 Required
#define and #undef shall not be used on a reserved identifier or reserved macro name

Rule 21.2 Required
A reserved identifier or macro name shall not be declared

Rule 21.3 Required
The memory allocation and deallocation functions of <stdlib.h> shall not be used

Rule 21.4 Required
The standard header file <setjmp.h> shall not be used

Rule 21.5 Required
The standard header file <signal.h> shall not be used

Rule 21.6 Required
The Standard Library input/output functions shall not be used

Rule 21.7 Required
The atof, atoi, atol and atoll functions of <stdlib.h> shall not be used

Rule 21.8 Required
The library functions abort, exit, getenv and system of <stdlib.h> shall not be used

Rule 21.9 Required
The library functions bsearch and qsort of <stdlib.h> shall not be used

Rule 21.10 Required
The Standard Library time and date functions shall not be used

Rule 21.11 Required
The standard header file <tgmath.h> shall not be used

Rule 21.12 Advisory
The exception handling features of <fenv.h> should not be used

Rule 22.1 Required
All resources obtained dynamically by means of Standard Library functions shall be explicitly released

Rule 22.2 Mandatory
A block of memory shall only be freed if it was allocated by means of a Standard Library function

Rule 22.3 Required
The same file shall not be open for read and write access at the same time on diﬀerent streams

Rule 22.4 Mandatory
There shall be no attempt to write to a stream which has been opened as read-only

Rule 22.5 Mandatory
A pointer to a FILE object shall not be dereferenced

Rule 22.6 Mandatory
The value of a pointer to a FILE shall not be used after the associated stream has been closed
