QA·C Help - 0777

	0777	[U] External identifier does not differ from other identifier(s) (e.g. '%s') within the specified number of significant characters.

Explicitly undefined		REFERENCE - ISO:C90-6.1.2 Identifiers - Implementation Limits

This identifier with external linkage is not distinguishable from other identifiers with external linkage within the parameters specified by the -XN and -XC options.

The -XN and -XC options should be configured to reflect (at least) the limitations of the implementation; but they may also be used to apply additional restriction. So for example:

The -XN option specifies the number of characters to be considered significant in an external identifier. The ISO:C90 Standard only requires an implementation to support 6 character significance - a severe restriction which reflects the limitations of linkers in 1990. The ISO:C99 Standard on the other hand requires an implementation to support 31 character significance. In practice, all modern compilers are likely to recognise 31 significant characters and possibly more. However, regardless of the capability of a particular implementation, it may still be considered desirable to restrict the number of significant characters to a smaller number in order to improve readability.
The -XC option specifies whether the implementation is able to distinguish lower and upper case characters when processing external identifiers. The ISO:C90 Standard does not require an implementation to be able to distinguish characters of differing case. Again this is a severe restriction, but is does not apply in ISO:C99 and it is very unlikely to be relevant to modern linkers.

Message 0777 is generated when identifiers cannot be distinguished within the limits imposed by these 2 options.

For example:


/*PRQA S 553,776,2017,3210,3408,3447 ++*/
/************************/
/* OPTIONS: -XN 10 -XC+ */
/************************/

extern int a234567890;                       /*      */
extern int a234567890a;                      /* 0777 */

extern int b234567890;                       /*      */
extern int B234567890;                       /* 0777 */

MISRA-C:2004 Rules applicable to message 0777:

Rule 1.2 (Required)	No reliance shall be placed on undefined or unspecified behaviour.
Rule 5.1 (Required)	Identifiers (internal and external) shall not rely on the significance of more than 31 characters.