QA·C Help - 2847

	2847	Apparent: Maximum number of characters to be written is larger than the target buffer size.

Arrays

An apparent anomaly has been detected.

Certain standard library functions specify a maximum number (M) of characters to be written to a char array (A).

function	A parameter number	M parameter number
asctime_s	1	2
ctime_s	1	2
snprintf	1	2
snprintf_s	1	2
strcpy_s	1	2
strncat	1	3
strncat_s	1	2
strncat_s	1	4
strncat_s	3	4
strncpy	1	3
strncpy_s	1	4

This message is issued whenever a non constant expression is used for M and its value is sometimes greater than the size of object A. This may result in an access outside the bounds of A.

For example, in the code shown below, the presence of the if statement suggests that m is likely to be greater than sizeof (a). Of course, if the value of m passed to function foo is never greater than 10, the upper bound of a will not be exceeded; but this would imply that the "if" statement is redundant and any code contained in the "if" block is also redundant.


/*PRQA S 1-9999 ++*/
/*PRQA S 2847 --*/

#include <string.h>

extern char a[10];
extern char b[11];

void foo (int m)
{
  if (m > sizeof (a))
  {
  }
  
  strncpy (a, b, m);   /* 2847 */
}

MISRA-C:2004 Rules applicable to message 2847:

Rule 21.1 (Required)

Minimisation of run-time failures shall be ensured by the use of at least one of (a) static analysis tools/techniques; (b) dynamic analysis tools/techniques; (c) explicit coding of checks to handle run-time faults

See also:

2845 Constant: Maximum number of characters to be written is larger than the target buffer size.
2846 Definite: Maximum number of characters to be written is larger than the target buffer size.
2848 Suspicious: Maximum number of characters to be written is larger than the target buffer size.

QA·C Source Code Analyser 8.1
MISRA-C:2004 Compliance Module 3.2
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