LANG.STRUCT.SE.SIZEOF : Side Effects in sizeof

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The operand of a sizeof operator has one or more side effects, or would have one or more side effects if evaluated.

Exception: sizeof(volLval) will not trigger a warning of this class if volLval is a volatile-qualified lvalue (and is not a variable-length array).

For the purposes of this check:

Function calls are always considered to contain side-effects unless one or more of the following is true:

the function is declared with GNU __attribute__((const)) or __attribute__((pure)), or
the function name matches a SIDE_EFFECT_FREE_FUNCTIONS rule.

All sub-expressions of the operand expression are checked, regardless of whether or not they will be evaluated.

Class Name

Side Effects in sizeof

Significance

style

Mnemonic

LANG.STRUCT.SE.SIZEOF

Categories

MisraC2023	MisraC2023:13.6	The operand of the sizeof operator shall not contain any expression which has potential side effects
Misra2012	Misra2012:13.6	The operand of the sizeof operator shall not contain any expression which has potential side effects
Misra2004	Misra2004:12.3	The sizeof operator shall not be used on expressions that contain side effects
AUTOSARC++14	AUTOSARC++14:M5-3-4	Evaluation of the operand to the sizeof operator shall not contain side effects.
MisraC++2008	MisraC++2008:5-3-4	Evaluation of the operand to the sizeof operator shall not contain side effects.
CERT-C	CERT-C:EXP44-C	Do not rely on side effects in operands to sizeof, _Alignof, or _Generic
CERT-CPP	CERT-CPP:EXP52-CPP	Do not rely on side effects in unevaluated operands
JSF++	JSF++:166	The sizeof operator will not be used on expressions that contain side effects.
JPL	JPL:19	Do not use expressions with side effects.

Availability

Available for C and C++.

Enabling

Checks for this warning class are disabled by default, and require the unnormalized C ASTs for the project. To enable them, add the following WARNING_FILTER rule and RETAIN_UNNORMALIZED_C_AST specification to the project configuration file.

RETAIN_UNNORMALIZED_C_AST = Yes
WARNING_FILTER += allow class="Side Effects in sizeof"

Note that retaining the unnormalized ASTs will increase the disk space used to store the project representation, and may make the analysis take longer.

#include <stddef.h>
int f(int i);

int lang_struct_se_sizeof(int a, volatile long int *vp){
      size_t i;

      i = sizeof(a);                                    /* no side effects in operand */

      i += sizeof(++a);                 /* 'Side Effects in sizeof' warning issued here */

      i += sizeof(*vp++);                                /* *vp++ is a volatile-qualified lvalue */
          
      i += sizeof(int[a]);                               /* no side effects in operand */

      i += sizeof(int[++a]);            /* 'Side Effects in sizeof' warning issued here */

      i += sizeof(f(a));                /* 'Side Effects in sizeof' warning issued here
                                         *  - a function call is always considered to be a side effect */

      i += sizeof((1==1)? *vp : *vp++); /* 'Side Effects in sizeof' warning issued here
                                         * - even though the increment will not be executed */
      return i;
}

The following configuration file parameters affect checks for this warning class.

LANG.STRUCT.SE.SIZEOF : Side Effects in sizeof

Summary

Properties

Example

Relevant Configuration File Parameters