strcmp() function implementation

[Sc0rp]

Hey,

How is the strcmp(char*, char*) implemented?
I need to implement it myself for my Comp Science class, and this is what I got:

int strcmp(const char* s1, const char* s2)
{
const char* p1 = s1 - 1;
const char* p2 = s2 - 1;

while (*++p2 == *++p1)
if (!*p2 || !*p1)
break;

if (*p2 > *p1)
return (-1);
else if (*p1 > *p2)
return (1);

return (0);
}


But it looks too long and clumsy for such a simple function.


Thanks.

[parksie]

You're close.

This is what's in the VC++ Runtime Library:int __cdecl strcmp (
const char * src,
const char * dst
)
{
int ret = 0 ;

while( ! (ret = *(unsigned char *)src - *(unsigned char *)dst) && *dst)
++src, ++dst;

if ( ret < 0 )
ret = -1 ;
else if ( ret > 0 )
ret = 1 ;

return( ret );
}

[MoMad]

Or better yet :D

int strcmp(const char* s1, const char* s2) {
int ret = 0;

while( !(ret = *(unsigned char*)s1 - *(unsigned char*)s2) && *s2 )
++s1, ++s2;

return ret != 0 ? (ret > 0 ? 1 : -1) : 0;
}

BTW: The turnary opperator is my fav :D
-MoMad

[Zaei]

That conditional makes it that much harder to read, with no extra speed =).

Z.

[parksie]

The ternary operator is only good for changing the emphasis from the comparison, to the result. For example:bool val = true;

if(val) {
cout << "true";
} else {
cout << "false";
}

cout << (val ? "true" : "false");The first way, the first thing you see is the comparison, but what's important is the fact that you're printing the value - the comparison is only a minor part of it (selecting the correct word to use).

[MoMad]

hey hey, hold on a sec!

Look, there are times to use if/else and times to use the turnery operator:


// try (1 line of code)
printf( "It is %d:%d %s\n", h, m, h < 12 ? "AM" : "PM" );

// instead of: (6 lines)
printf( "It is %d:%d", h, m );

if( h < 12 )
printf( " AM\n");
else
printf( " PM\n");



The above strcmp example doesnt make any difference, but its completely valid, and hey, like the recruiting ppl say, the more complicated your code, the smarter ppl will think you are :D

Anyways, I am saying that ternery operator is AWESOME!! Better than if/else but everything has its rightious moments. Parksie you are soooo right, and you too Zaei; this was not the right problem for a ternery operator, but I just wanted to show everyone how you can make your code as little as possible ;) Like the while loop, it could have been done with for's and more writing but it was done with 2 lines instead of 10 or say 30, you see where im getting at??

[kedaman]

Originally posted by MoMad
but its completely valid, and hey, like the recruiting ppl say, the more complicated your code, the smarter ppl will think you are :D

I would prefer the ternary operator for elegance purpose only, I find fachinating expressions with sideeffects a beauty. However, complex expressions are often a performance hit, so it's not too often, except for some pointer aritmetic when you get to use your l337ness for practical purposes as well ;)

But, I'm going to change that, when you realize the beauty of my expression templates :)

[MoMad]

Kedaman, Shout me a holla when you're done with that, will ya?? And hey, it depends on how you use it... I havent come across "side-effects" but then again, I dont "overdose" on the ternery operators... so when I do, ill let you all know.

Aaaaagggghhhh, reading back, my spalling is ewfall!! Argggggg...

[Sc0rp]

Thanks a lot everybody. ;)

[Sc0rp]

Alright, that's my final version.
The HEAVY HEAVY commenting is required by the testers. :o


// -----------------------------------------------------
// Function Name: strcmp()
//
// Input: Two strings to compare.
//
// Output: (-1) the second string is bigger.
// ( 1) the first string is bigger.
// ( 0) the strings are identical.
//
// Operation: The function receives two strings to
// compare in dictionary-comparison, and
// returns a flag according to which
// string is bigger.
// -----------------------------------------------------
int strcmp(const char* p1, const char* p2)
{
// A variable to hold the distance in ASCII charcters
// between the current two characters we're comparing.
int dist = 0;

// Keep checking while the distance is 0, and we're
// not hitting NULL on one of the strings.
while (!dist && *p1 && *p2)
// Get the distance while incrementing the
// pointers to the next character.
dist = (*p2++) - (*p1++);

// Check the last distance and according to this
// return (1) if the first string is bigger, (-1)
// if the second string is bigger, or (0) if the
// strings are identical.
if (dist > 0)
return (-1);
else if (dist < 0)
return (1);

return (0);
}


I didn't find any bugs, but if anyone does...

[parksie]

The javadoc style commenting is liked in a lot of commercial instances (Java, KDE, stuff like that), and it's in some ways easier to type:/** Compare two strings.
\param p1 First string
\param p2 Second string.

\return A flag determining which string was bigger.
\arg -1 the second string is bigger.
\arg 1 the first string is bigger.
\arg 0 the strings are identical.

\remarks The function receives two strings to
compare in dictionary-comparison, and
returns a flag according to which
string is bigger. */
int strcmp(const char* p1, const char* p2) {
// ...
}This is just one way of doing it though, some people prefer different styles :)

[MoMad]

Hey Parksi, isnt it like:

@param string p1 - first string
@return int - blah blah

hmm... there are tons of different styles, but actually the way he has it is most popular among C/C++ programs and its even a standard at my school hehe :D I hear the Java commenting styles are also used by many php and perl programmers :P

[parksie]

You're probably right.

I use Doxygen though, which does @ and \. (I think \ is for Qt).

I wasn't saying there was a problem with his, it's just you can't easily separate the documentation from the code with that style.

www.doxygen.org

[MoMad]

Yes you are right...

[kley]

Here, nice and simple:

int strcmp(char *str1, char *str2)
{
int i;
for (i=0;str1[i]==str2[i];i++)
if (str1[i] == '\0') return 0;
return str1[i] - str2[i];
}

[general74]

Is it better..?

int strcmp(const char* a, const char* b)
{
while(*a++ == *b++)
if(*a == '\0' && *b == '\0') return 0;
return -1;
}