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

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 lower case 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 8.12 Required 
Within an enumerator list, the value of an implicitly-specified enumeration constant shall be unique
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 noninteger 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 20.6 Required 
Tokens that look like a preprocessing directive shall not occur within a macro argument
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 fi rst 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
