"Reverse" bytes in string

[BlueAnaconda]

Hello,

I have a string like this : "ABCDEF"

I want to get this from this string : "EFCDAB".

What's the best way to do that in CVI ?

Thanks in advance,

Blue

[altenbach]

You are reversing 16bit words, not bytes here.

[RobertoBozzolo]

Something along this line? (str1 and str2 must be previously allocated in the correct size)

for (i = 0; i < strlen (str1); i++) {
	str2[i] = str1[strlen (str1) - i - 1];
}

[gdargaud]

This is more a C question than a CVI question... You can do this in place without need for an extra allocation by using an intermediate short. Something like (untested, caveat if string len is odd, caveat if UTF, etc)

char Str[]="ABCDEF";
int L=strlen(Str);
short C, *SC=(short*)Str;
for (int i=0; i<L/4; i++) {
 C=SC[i];
 SC[i]=SC[L/2-i];
 SC[L/2-i]=C;
}

[BlueAnaconda]

Hello,

Roberto, this will gave me "FEDCBA" and not "EFCDAB".

[BlueAnaconda]

Hello gdargaud,

I will try this, thank you. 

[RobertoBozzolo]

---

@BlueAnaconda  ha scritto:

Hello,

Roberto, this will gave me "FEDCBA" and not "EFCDAB".

---

Correct, I didn't focused on expected target string and the quotes around "reverse"

[BlueAnaconda]

gdargaud, 

The code I tested, it's not good too.

Roberto, Yes, do you have a suggestion please ? 

[carlox]

This should work for any string with any number of couples of chars.
The lack of explanations and comments is not casual. 🤣

    char *s = "ABCDEF";
    int len = (int)strlen(s);
    int len2 = (len / 4) * 2; // ;-)

    char c1, c2;

    for (int i=0; i<len2; i+=2) {
        c1 = s[i];
        c2 = s[i+1];
        s[i]   = s[len-2-i];
        s[i+1] = s[len-1-i];
        s[len-2-i] = c1;
        s[len-1-i] = c2;
    }

[RobertoBozzolo]

You can also make use of SwapBlock function in the Programmer's Toolbox:

#include "toolbox.h"
#include <ansi_c.h>
static int		i, len, duplets;
static char	str[64];

strcpy (str, "ABCDEFGHIJKLMNOPQRSTUVWXYZ");
len = strlen (str);
duplets = len / 2;

for (i = 0; i < duplets; i += 2) {
	SwapBlock (str + i, str + len - i - 2, 2);
}

Just my 2c... after my initial gaffe 😉