Programming Forums > Application Development > C

bl00dninja · Apr 2nd, 2006, 5:20 PM

from the k&r

void strcpy(char *s, char *t)
{
      while((*s++ = *t++) != '\0');
}

obviously this code copies one string to another, but my question is..."do C programmers really code like this?" reading the K&R has enhanced my thoughts of what can be done with a line of code, but they seem to praise code like ths when it can be done in a few more lines with a sense of clarity. (they do give examples of such code).

THE REAL DEAL...are they saying this is good coding practice, or are they coming from the 1960's+ UNIX environment where this counterintuitive crap was a necessity because of low memory capabilities?

either way, you gotta love the simplicity of placing so many operations on one line. i would highly reccomend this book to any coder.

jim mcnamara · Apr 2nd, 2006, 6:52 PM

The big problem with C is obfuscation.

I've been writing C for a long time. Stuff like that is cool - but not a good idea.
Unfortunately because it's in K&R it has a sort of special appeal to C programmers.

DaWei · Apr 2nd, 2006, 7:10 PM

Quote:

coming from the 1960's+ UNIX environment where this counterintuitive crap was a necessity because of low memory capabilities?

Yup. Personally, I would have written it in even shorter form.

Jimbo · Apr 2nd, 2006, 9:26 PM

Isn't the != '\0' part unnecessary?

Navid · Apr 2nd, 2006, 9:46 PM

Quote:

Originally Posted by Jimbo

Isn't the != '\0' part unnecessary?

*t is being copied into *s until it finds '\0' in *t. If it weren't for the condition != '\0', it would continue copying into *s past from the string that t is pointing to, whatever that's in memory there. Plus, if there's no condition; how would the loop end? '\0' determines the end of a string.

Jimbo · Apr 2nd, 2006, 10:41 PM

its in C, where everything is implicitly cast to a boolean value, and any non-zero value is true

Navid · Apr 3rd, 2006, 12:45 AM

You're right, it is unnecessary, but I don't understand why myself. How will (*s++ = *t++) ever return 0?

Polyphemus_ · Apr 3rd, 2006, 1:28 AM

An assignment operation always returns the new value of the object to assign, so someVariable = 3 would return 3 (return is not the good word here, I know, but I don't know anything better). When you assign *s++ = *t++, you assign *t to *s, t and s are increased, and it returns the new value of s, so if it is the null character, '\0', which is equal to false.

nnxion · Apr 3rd, 2006, 3:13 AM

Quote:

Originally Posted by Jimbo

Isn't the != '\0' part unnecessary?

It is necessary, you don't make a compare with (*s++ = *t++), you assign. So that would always return true. Unless you assign it false, but you don't because characters are greater than 0. So would never stop and you would write beyond your string, which in turn will probably get you a segfault or something else bad.

grumpy · Apr 3rd, 2006, 3:44 AM

Quote:

Originally Posted by nnxion

It is necessary, you don't make a compare with (*s++ = *t++), you assign. So that would always return true. Unless you assign it false, but you don't because characters are greater than 0. So would never stop and you would write beyond your string, which in turn will probably get you a segfault or something else bad.

Incorrect. An assignment is an expression that yields the value assigned.

If we do

(Toggle Plain Text)

    result = (*s++ = *t++);

it is exactly equivalent to;

(Toggle Plain Text)

   result = (*s = *t);
   ++s; ++t;   /* the post increments */

or (with some oversimplification to avoid doing multiple assignments in one line of code);

(Toggle Plain Text)

   *s = *t;
   result = *t;
   ++s; ++t;   /* the post increments */

All of this means that the code

(Toggle Plain Text)

void strcpy(char *s, char *t)
{
      while(*s++ = *t++);
}

achieves exactly the same thing as;

(Toggle Plain Text)

void strcpy(char *s, char *t)
{
   int result = 1;   /* start non-zero */
   while (result)
   {
         *s = *t;
         result = *t;
         ++s; ++t;  
   }
}

Note: the standard strcpy() returns it's first argument, not void.

As to the question of whether such code is good practice ..... it was sort-of desirable a couple of decades back due to limited memory and capacity of compilers to handle large bodies of code, but people tended to go overboard with it and make unreadable code. Now, readability is more important as programmer time is more expensive than extra memory for a computer.

Apr 2nd, 2006, 5:20 PM	#1
bl00dninja Programming Guru Join Date: Oct 2004 Location: namespace std Posts: 1,246 Rep Power: 5	whitebook from the k&r (Toggle Plain Text) void strcpy(char s, char t) { while((s++ = t++) != '\0'); } void strcpy(char s, char t) { while((s++ = t++) != '\0'); } obviously this code copies one string to another, but my question is..."do C programmers really code like this?" reading the K&R has enhanced my thoughts of what can be done with a line of code, but they seem to praise code like ths when it can be done in a few more lines with a sense of clarity. (they do give examples of such code). THE REAL DEAL...are they saying this is good coding practice, or are they coming from the 1960's+ UNIX environment where this counterintuitive crap was a necessity because of low memory capabilities? either way, you gotta love the simplicity of placing so many operations on one line. i would highly reccomend this book to any coder. __________________ i put on my robe and wizard hat... Have you ever heard of Plato, Aristotle, Socrates?...Morons.

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Apr 2nd, 2006, 6:52 PM	#2
jim mcnamara Hobbyist Programmer Join Date: Jun 2005 Location: New Mexico Posts: 228 Rep Power: 4	The big problem with C is obfuscation. I've been writing C for a long time. Stuff like that is cool - but not a good idea. Unfortunately because it's in K&R it has a sort of special appeal to C programmers.

Apr 2nd, 2006, 9:26 PM	#4
Jimbo Battle Programmer Join Date: Feb 2006 Location: Bellevue, WA, USA Posts: 754 Rep Power: 3	Isn't the != '\0' part unnecessary?

Apr 2nd, 2006, 10:41 PM	#6
Jimbo Battle Programmer Join Date: Feb 2006 Location: Bellevue, WA, USA Posts: 754 Rep Power: 3	its in C, where everything is implicitly cast to a boolean value, and any non-zero value is true

Apr 3rd, 2006, 12:45 AM	#7
Navid Hobbyist Programmer Join Date: Feb 2005 Location: Canada Posts: 187 Rep Power: 4	You're right, it is unnecessary, but I don't understand why myself. How will (s++ = t++) ever return 0?

Apr 3rd, 2006, 1:28 AM	#8
Polyphemus_ Expert Programmer Join Date: Aug 2005 Location: Rotterdam, the Netherlands Posts: 942 Rep Power: 4	An assignment operation always returns the new value of the object to assign, so someVariable = 3 would return 3 (return is not the good word here, I know, but I don't know anything better). When you assign s++ = t++, you assign t to s, t and s are increased, and it returns the new value of s, so if it is the null character, '\0', which is equal to false.

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Programming Forums > Application Development > C

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