QA·C Help - 3701

	3701	Implicit conversion: char to unsigned char.

Arithmetic type - Implicit conversions

An expression of type char is being implicitly converted to type unsigned char.

Implicit type conversions of this nature can occur in the context of:

initializations
assignment operations
the passing of a function argument
the return of a value from a function

In the C language there exist 3 distinct char types:

signed char
unsigned char
char (often referred to as "plain char"

It is recommended that signed char and unsigned char should be used for "numeric" data and plain char should be used for "character" data. Numeric data can be stored in type char but the range of values will be implementation-defined because the type is sometimes implemented as a signed type and sometimes as an unsigned type. Likewise, character data can be stored in type signed char or type unsigned char, but it is more sensible to use type char.

For example:


/*PRQA S 2017,3197,3199,3203,3227,3408,3447,3602,3625 ++*/


extern void ef(unsigned char p);

extern unsigned char foo(char v)
{
    unsigned char a = v;        /* Message 3701 */

    a = v;                      /* Message 3701 */

    ef(v);                      /* Message 3701 */

    return v;                   /* Message 3901 */
}

No MISRA-C:2004 Rules applicable to message 3701