Thread: strcmp() \ flushing output

Platform : WindowsXP
Compiler : VC++ 6


Question 1 :

Here's a program using strcmp() :

Code:

#include <stdio.h>
#include <string.h>

int main(void)
{
	char s1[50], s2[50];

	printf("s1 : ");
	fgets(s1, sizeof(s1), stdin);

	printf("s2 : ");
	fgets(s2, sizeof(s2), stdin);

	
	if(strcmp(s1, s2) == 0)
		printf("s1 == s2\n");
	else if(strcmp(s1, s2) < 0)
		printf("s1 is less than s2\n");
	else if(strcmp(s1, s2) > 0)
		printf("s1 is greater than s2\n");


	return 0;
}

I already know what strcmp() does , but my question is how does it actually compare the two strings? if you enter "aa" as s1 and "AAAAAAAAA" as s2 (for example) ; strcmp() would return '+1' wich means s1 is greater than s2



Question 2 :

I never had to flush the output buffer in my programs before, because they seemed to run well and updating ouput as they should. But some programmers told me that some systems won't update the output untill it recieves a new line (\n) or when the output is manually flushed with fflush(stdout), Is this true? and if so , is this the only reason that programmers need to flush output?



Thanks in advance

1) strcmp doesn't care about the length of the string, if that's what you're asking. it compares the strings until it encounters unmatching characters (or the null-terminator of one of the strings). strcmp() considers 'a' to be greater than 'A'. the function is used often for sorting strings of course.

2) flushing output buffers isn't always necessary, but it never hurts, either (especially with files).

[edit]
beat me to it (I actually like your explanation better anyway )
[/edit]

so strcmp() uses the ASCII\EBCDIC table and compare characters by their value, right?

Not really. He's a simple one:

Code:

int strcmp(const char *s1, const char *s2)
{
  while (*s1 && *s2)
    if ( *s1 != *s2 )
      break;
    else
    {
      s1++;
      s2++;
    }
  return *s1 - *s2;
}

Of course there are versions that do it in fewer lines and faster but this should show you how its done

I'm afraid that your strcmp() shows 'aaa' less than 'AAAAAA' and returns -65 .

I tried to make my own and here's what i got :

Code:

int mystrcmp(const char *s1, const char *s2)
{
  for( ; *s1 != '\0' && *s2 != '\0'; s1++,s2++)
  {
	  if(*s1 > *s2)
		  return 1;
	  else if(*s1 < *s2)
		  return -1;
  }

  return 0;

}

It works exactly like strcmp() (i mean produce the same results) , but i don't know if my comparsions are valid (the > and < between characters) , are they?