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Note that the two different ways a character is used as an int (as an unsigned char + EOF, or as a plain char, converted to int) can lead to confusion. For example, isspace('\200') results in undefined behavior when char is signed.
Recommendations
STR00STR07-A. Use TR 24731 for remediation of existing string manipulation code
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ARR38-C. Do not add or subtract an integer to a pointer if the resulting value does not refer to an element within the array 06. Arrays (ARR) STR00STR07-A. Use TR 24731 for remediation of existing string manipulation code