Looping through an array with pointer notation

Question

I'm learning pointers in C++, while not as clear as I'd like to be on the subject, I'm slowly getting there.

My goal here was to write a function using pointer notation, to go through an array and change the case of the input.

For example

("ab7d") myToUpper() -> AB7D

Here is my idea for accomplishing this.

void myToUpperCase(const char *source, char *dest)
{
    for (int i = 0; *(source + i) != '\0'; i++)
    {
        *(dest + i) = toupper(* (source + i));
    }
}

Results

("ab7d") myToUpper() -> AB7D\377

Would someone mind explaining the reasoning behind \377 being added to the output, obviously I'm looking for just the source to be changed here with nothing else added to the output.

Thanks

why not using iterators and better..why not for_each and lambaded toupper? — Joel
– Joel, Commented May 15, 2016 at 21:45
Also beware of potential toupper UB. stackoverflow.com/questions/21805674/… — Baum mit Augen
– Baum mit Augen ♦, Commented May 15, 2016 at 21:45

rpy · Accepted Answer · 2016-05-15 21:54:27Z

Strings are char arrays with a '\0' byte as a terminating character.

Your code is copying anything but the final '\0' byte. So, if you chnage your code to terminate dest with a \0' byte all will be fine. (The '\377' you are observing just is the byte that happens to occur at that position in dest.)

eg. you could change your code to:

void myToUpperCase(const char *source, char *dest)
{
    for (int i = 0; ; i++)
    {
        if (*(source + i) == '\\0') 
        {
            *(dest + i) = *(source + i);
            break;
        }
        else
        {
            *(dest + i) = toupper(* (source + i));
    }
}

You might also try another solution without any index i based on :

while(*source++ = *dest++) /* empty body */;

(Purists (validly) might flag using side effects within loop conditions as bad smell! But it just should give an idea....)

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