Case conversion in C

itsme86 · 09-12-2005, 10:43 AM

Code:

for( x = 0; x < strlen( the_string ); x++ )

I really hope you guys don't write code like that. The use of strlen() there is very inefficient. For short strings like "abc123" it doesn't really matter, but bad habits die hard. A much better way to control the loop would be:

Code:

for( x = 0; the_string[x]; x++ )

If you don't understand why just ask and I'll be happy to explain.

Matir · 09-12-2005, 11:24 AM

A valid point, evaluating the expression strlen() on each loop is bad. My code was only intended as an example, and I felt that strlen() illustrated the point better.

Dark_Helmet · 09-12-2005, 01:45 PM

Not to send this thread down a coding style path, but...

Yes, bad habits die hard. I definitely still have some myself. However, I think

Code:

for( x = 0; the_string[x]; x++ )

is another bad habit. It's a bad habit because of exactly what itsme86 did after posting it: offered to explain it. If it's not readily understandable at face value or with sparse comments, then there's a better implementation. I would argue this combination of methods is better:

Code:

char *the_string;
unsigned string_length;
unsigned character_id;

...

string_length = strlen( the_string );
for( character_id = 0; character_id < string_length; character_id++ )

Just my thoughts on the subject.

Matir · 09-12-2005, 03:13 PM

I would agree. Just be careful on the chance that your loop might dynamically modify the string: then your length would be off.

zaichik · 09-12-2005, 04:55 PM

Well, this thread has served its initial purpose, so if it gets taken down other, unforeseen paths, that's fine by me.

I do see why calling strlen() each interation would be a bad thing, and actually implemented it front of the loop a la Dark_Helmet's suggestion.

The only thing I don't get is itsme86's idea for the loop control:

Code:

for( x = 0; the_string[x]; x++ )

Clearly I don't understand memory allocation well enough, but I don't see how the_string[x] can be guaranteed to return true until we start accessing elements outside its allocated space.

I'd love to hear the explanation, itsme86.

itsme86 · 09-12-2005, 06:16 PM

A string in C is an array of characters terminated with an ASCII 0. So "hello" in memory looks like 'h', 'e', 'l', 'l', 'o', '\0'.

Characters are really just tiny ints and 0 always marks the end of the string. This is also why to hold a 5-letter string like "hello" you need an array that can hold 6 elements. You need to make room for that '\0' at the end.

I hope that explains it well enough.

zaichik · 09-12-2005, 06:55 PM

Ding. Light bulb goes on.

Not outside of its allocated space, but until we hit the null character(i.e., false).

Of course. Thanks for the explanation.