Discuss StrToUpper code

Discuss the following code:

/*
 * Converts an lower case letter into an upper case letter.
 * If the letter is not lower case, it does nothing.
 * In ASCII, upper case letters come before lower case
 * letters ('A' is 65, 'a' is 97) so we need to subtract
 * to convert.
 */
#define MAKE_UPPER_CASE(c) \
 (((c > 'a') && (c < 'z')) ? (c - ('a' - 'A')) : c)

/*
 * StrToUpper -
 * Converts a string to be in all upper case. Returns a pointer
 * to the new, null-terminated, all-upper-case string.
 */
char *StrToUpper(const char* str)
{
    char upperCaseString[1000];
    int i = 0;

    while (i < strlen(str)) {
        upperCaseString[i] = MAKE_UPPER_CASE(str[i++]);
    }

    return upperCaseString;
}

Macro

• Does not evaluate expressions before passing to macro. Thus, i++ will get executed for each appearance of c in MAKE_UPPER_CASE.


• Better to use inline function for type-checking


• (c - ('a' - 'A')) could be replaced by c + 32 for performance


• c > 'a' and c < 'z' should be that and equal to

Function

• Uses local storage: May be garbage because program may overwrite later on. Should either dynamically allocate return string or have input a string buffer as a parameter.


• Does not append '\0' (null) character


• upperCaseString[1000] can only contain 1000 chars and a large input str will cause buffer overflow.


• int i may overflow if str is large


• strlen() can be pulled out of the while statement so it won't be executed each time through the loop