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Programming-Idioms

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  • Obj-c

Idiom #41 Reverse a string

Create the string t containing the same characters as the string s, in reverse order.
The original string s must remain unaltered. Each character must be handled correctly regardless its number of bytes in memory.

Turning the string "café" into "éfac"
@import Foundation;
NSMutableString *t=[NSMutableString string];
[s enumerateSubstringsInRange:NSMakeRange(0,s.length)
  options:NSStringEnumerationReverse|NSStringEnumerationByComposedCharacterSequences
  usingBlock:^(NSString *part, NSRange r1, NSRange r2, BOOL *stop) {
    [t appendString:part];
}];
#include <stdlib.h>
#include <string.h>
char *strrev(char *s)
{
	size_t len = strlen(s);
	char *rev = malloc(len + 1);

	if (rev) {
		char *p_s = s + len - 1;
		char *p_r = rev;

		for (; len > 0; len--)
			*p_r++ = *p_s--;
		*p_r = '\0';
	}
	return rev;
}

Returns NULL on failure

New implementation...
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